AGRICULTURAL CHEMISTRY.

Otago Witness, Issue 2103, 14 June 1894, Page 11

AGRICULTURAL CHEMISTRY.

A SERIES OF LECTURES DELIVERED BY PROFESSOR BLACK AT THE OTAGO UNIVERSITY. V.— Sulphur.— A Practical Demonstration at Kejipthorne-Prosser's N.Z. Dnuo Company's Works at Burnside. This element is found in small quantities in all cultivated plants. It must, therefore, be taken as a necessary part of their mineral food which they take from the soil. In the Eoil it exists chiefly as sulphates of lime, magnesia, potash soda, and ammonia. Superphosphate of lime — so largely used everywhere as one of the beat kinds of artificial manures— contains from 20 to 45 per cent, of sulphate of lime, and nearly a fifth of this is sulphur, so that a ton of superphosphate contains from 901b to 2001b of sulphur in a soluble stite, and therefore in a condition to supply both sulphur and lime to the plauts in an available form. There is another manure, under the name of kainit, in the market, which also offers sulphur in a soluble condition combined with potash as sulphate of potash. This manure will be described under the potash salt?, as that element, and nob sulphur, is its most valuable constituent. Sulphur itself, found in large quantities in old or recent volcanic regions — Sicily, Iceland, South Italy, and in New Zealand at Tarawera and White Island off the coast of Aucklandis now being made in nature by the meeting of two poisonous common colourless volcanic gases of a powerful, penetrating, aud mosb disagreeable odour. These gases are sulphur dioxide — SO 2 — and sulphuretted hydrogen— H 2 S. The equation is SO 2 + H 2 S = 2H 2 O + SJ. The immediate result of the meeting of the c c two gas^s is the formation of liquid water and solid sulphur. Chemistry does not offer a better example of the wonderful transformations which take place when two substances act chemically on each other. The lecturer had seen the sulphur, manufacturing process in full operation in the It jtomahana district just before the Tarawera volcauo burst out. There the two gases named were issuing separately from their respective crevices and meeting in the air, the result being a yellow mist of sulphur perpetually forming and falling on tho barren mixture of sulphur and sand that has to pass for soil in that desolate region. Sulphur was made on the letture table by this process, constituting ono of the prettiest experiments of the course. The sulphur dioxide was made by boiling in a glass flask stroDg sulphuric acid with copper ; and the sulphuretted hydrogen by the action of dilute sulphuric acid on sulphuret of iron in another glass flask. From each flask the gas was led into a series of three clear glass globes, where they mingled, producing by their union, as if by magic, a dusty white cloud in each of the globes, which Boon coated them with a coating of pure yellow sulphur. The great part which sulphuric acid plays in the manufacture of artificial manures, as well as in many other very important industries, makes it necessary for us to know something of its own manufacture. Though it was known to the alchemists of the Middle Ages, it was not till the present century had well begun that any considerable quantity began to be made. Its application to the manufacture of bleaching powder (chloride of lime) and washing soda gave this acid a firm footing among the large industries of Europe ; and then the increasing demand for nitric acid and acetic acid, which are products of its action on saltpetre and acetate of soda respectively, gave it a further impulse. TheD, again, the more recent discovery or invention of the coal tar colours (aniline, mauve, magenta, alizarn, picric acid, &c), guncotton, and nitroglycerine, in all of which it is a prime factor, created for this acid a demand which is now Bupplied by the production of about a million tons per annum around the great industrial centres of Manchester, Glasgow, and Newcastle. So numerous and varied and vast are its applications in the great modern industries of civilised communities that it has been well said of this acid that the amount oF a nation's consumption of it may bo taken as a gauge of its industrial activity and a measure of its civilisation. In Otago there is the one sulphuric acid woiks ab Burnside, with an output of about 500 tons per annum Taking the population of Otago at 160,000. this would give us about onetweltth of the English production per head of the population. The manufacture i 3 carried on iv large chambers made of heavy sheet lead— 7lb to the square foot. No solder can be used for joining the sheets of the metal, for no solder could withstand the action of the fumes that are concerned in the manufacture. The contiguous sheets are therefore joined together by a portion of tho lead of each sheet being molted and run together by running the hot fhme from a blowpips slowly along the junction. Tnis melted metal on hardeiiing B (which it does very readily) forms a homogeneous folder of lead itselfj.and is just as strong aud effectual agaiust the action of the fumes as any other pirb of the chambers. Iv these chambers — often 100 ft long by 20ft wide iind 18?t high aud communicating with each other hj wide lead pipes beat twice ab right angles and just protruvling through the roofs of two contiguous chambers — sulphuric acid is made by the action of four ga3es on each other. These gases are (1) sulphur dioxide — SO 2 — which is made by roasting either sulphur or pyrites (the mundic of miners) in a suitable furnace. The sulphurous fumes are led by a short flue into the first of tho chambers. (2) The brown oxides of nitrogeu. These are made in a small iron pot containing Chili saltpetre and sulphuric acid, the pot and conteuts being hsscted by the heat of the sulphur furnace, on a ledge of which it is placed so as to have the hot sulphurous gases streaming over it. These nitrous fumes pass into the lead chamber with the sulphurous fumes. (3) Oxygen. This gas is supplied by the air that feeds the sulphur in the sulphur furnaces. Part of the oxygen of the air is, of course, used up in burning the sulphur, aud the res.t of it goes into the chamber with tho other fumes. (4) The last requisite is steam, which is projected into the chambers at various points from a boiler. The seam from the boiler id led in a 4in pips rouad outside the chambtr?, ar.d from this pips smaller branch pipes project just in through the lead walls of the clip-mbers, delivering tho steam iv such quantities as may be required. The action on each other of these four gases wtrch recult-- in the formation of sulphuric acid in these lend chambers in something of this kind-(-j) The sulpbur dioxide— SO 22 — has room for another atom of oxygen which would make it sulpbur trioxide— SO., ; but it is not disposed to take that extra atom of oxygen from the atmospheric air iv the chambers, (b) The brown nitrous fumes, however — NO 2 and N.,,0,, —have each one atom of oxygen that they can

1 easily spare. They therefore pa3B this oxygen over to the SO 2f as shown by the equations— SO 2 + N0 2 = NO + SO;, ! SO 2 + N20.(N 2 0. ( = 2NO + SO 3 Tho 6ulphur N trioxide thus formed has a most intense attraction for water in any form, and therefore instantly unites with Iho 6team in the chambers, forming with it sulphuric acid by the equation — SO n + H 2 O = H 2 SO, The sulphuric acid, H 2 SO,, thus produced, being heavy, falls on to the lloor of the chambers and mingles with the cold water there. Meantime the oxide of nitrogen (NO) formed by the surrender of oxygen by the brown fumes, as shown above, takes another atom of oxygen from the air : NO + O = NO 2 and 2 NO + 0 = N20.,,N 2 0.,, thus becoming brown again and ready to hand over the newly-picked-up oxygen to sulphur dioxide ; and so the thing goes on — sulphur dioxide always pouring in from the sulphur furnaces, perpetually taking oxygen from the brown fumes, and then uniting with the water sent in as steam. The excess of fumes passes from the first to the second chamber by the wide pipe connecting them through their roofs, and from the second to the third, so that there may be ample time and room for all the fumes to complete the formation of acid. Tho sulphuric acid is allowed to accumulate on the floors ot the chambers till it is pretty strong, containing about 60 per cent, of acid and 40 of water. Io is then drawn off by a leaden syphon pipe as "chamber acid," in which condition it is strong enough to be used for many manufacturing processes. The chamber acid ia brought up to a strength of 76 per cent, in leaden pans heated either below or above, the heat driving off part of the water in the form of steam and leaving the acid itself behind in the pans. The acid thus strengthened to 76 per cent, is known in the trade as brown oil of vitriol, and labelled B O.V. To get the pure, strongest acid — the real cil of vitriol containing 98 per cent, of acid — glass retorts or platinum stills are employed, as auy of the cheaper metals — iron, lead, copper, silver, &c— would bo attacked and destroyed by the hot strong acid. In these distilling processes 3 it is the water that is evaporated off and passes away, the sulphuric acid itself remaining behind in the stills. This is just the opposite of what takes plico in the distillation of alcoholic liquors, when it is chiefly the spirit that is evaporated off — the water maiuly remaining in the stills. The strong sulphuric acid or oil of vitroil thus made is a heavy oily liquid, nearly twice as heavy as the samebulkof water. Ib is about the strongest acid known, dissolving and destroying

all the common metals except gold and platinum, charring wood, paper, leather, and all kinds of clothing materials, cottous, linens, woollen goods of every kind aud quality — burning and charring the flesh of animals, and dissolving even their bones, breaking up sugar by separating out its charcoal from the elements of water and appropriating the latter to itself. These and many other wonderful things this mostlpowerful of acids does rapidly and silently, ever leaving destruction in its p^th. But this very power is, when properly applied, a source of incalculable bsn< fits to the human race. The visit cf the lecturer and bis students to Burnside last Saturday had athree fold object : first, to see the manufacture of sulphuric acid itself ; second, to see the application of that acid to the manufacture of muriatic acid (spiiits of salt) and nitric acid (aqua fortis), acstic acid, ammonia, and fiuoevphosphate, all cxrried on at K>nipthorne, Prosser, iud Co.'s chemical and mauure wo ks ; atd 3rd to sic through the freezing works, with its cold chambers and powerful air-compressing machin> ry. The class mustered at Burnside to the number of about 60 members, including 12 lady students. Several of them had come long distances for the occasion — getting up at 4 o'clock in the morniDg, starting for the railway station at Clinton, Lawrence, or Palmerston at 5 o'clock to catch the early train at 6 to 6 30, reaching Dunedin any time between 10 and 12, and getting back to their homes again between 7 and 10 p.m. This is the usual Saturday programme of eeveral of the members of tho teachers' class. They were received and heartily welcomed by Mr Smith, the manager at tho chemical works, who proceeded at once to guide them through the various departments under his control. The lead chambers here are three iv number, 40ft long by 14ft wide and 12tb high. There are four sulphur furnaces, all contained in one piece of ii re-brick masonry, and fitted wit'-i slidiDg iron doors that cm be adjusted so as to regulate the admission of air— much or little at pleasure, according to the requirements of the chambers. All the furnace 3 unite their gaseous eulpurous load ia one co'jiruon flu", along which they pour it inlo chamber No. 1. Expose;! to these hot blue fumes the nitre poba emit their deadly brown vapours, which are carried along with them into the chamber, there to mingle with tha steam hurled in afc various points from the boiler alongside. The air in the buUdiug outside the sulphur furnaces is not at all uncomfortable, notwithstanding tho deadly nature of the operations within. The sulphur burned is now got from the. Tarawera volcanic hot springs district, the Sicily importation having stopped some time ago. The

nitre for the pots is the Chili saltpetre (nitrate of soda), which is cheaper than ordinary potash saltpetre and yields more gas, weight for weight. Here nothing is wasted, the refuse of theso saltpetre pots being utilised afterwards for enriching some of the bouedust with soluble sulphate, aud for rendering part of the bones themselves soluble. From the lead chambers they saw tho acid led down in a leaden pipe to the platinum still. This still, made of one piece of pure platinum, is 4ft long by Ift or 18in wide, and is heated beneath by the flames from the furnace over which it is built. The water is expelled in vapour, and the strong acid is perpetually flowing out through a platinum syphon into a second smaller reservoir, from which it runs through a platinum tube into a cooler surrounded by cold water, and is thence conveyed in a perpetual steady, slender, oily stream into the 3gal stone jars, ready for use or for tho market. The platinum still and appliances must have cost over £1000, and would be worth now nearly double that sum owiug to the recent large rise in the price of that metal. The next department visited was the muriatic acid and nitric acid plant. Here was to bo seen, though not in operation on this particular day, the cast iron pan which receives the common salt from which the acid is to be made. This pan 13 built into the masonry of a furnace in such a way that the flames will strike the bottom of ib in a uniform manner. Strong sulphuric acid is led into tho pan by a leaden pipe and poured in a thin stream, slowly ab firjr, over the salt. Chemical action of a very vigorous kind instantly is set up ab the firat contact of the acid with the salt ; dense volumes of the heavy grey muriatic acid vapour are produced and pour out through the pipe leading into the Woulffe's bottles placed in series alongside. These Woulff c's bottles have a capacity of sgal or 6gal. Bach of them is about two-thirds full of clean cold water to begin with, and each of them has two necks. Through one neck — that nearest the furnace or pan — the delivery tube conveying the fumes passes down into the cold water, and there delivers its muriatic acid vapours. The vapour is condensed and dissolved by the water as fast as ib comes in. This goes on for some time till the water in that first Woulffs's bottle i 3 nearly saturated with the vapour, and then it begins to rise through the water into the roof of that bottle, whence it is led by another pipe (which just protrudes through tho second neck) away into Woulffe's bottle JNo. 2 This, in its turn, gets charged aud saturated with the muriatic acid, and tho excess of the gas is in like manner passed into the third and fourth, and so on up to the, twelfth Woulffe's bottle, the contents of each becoming converted into the "hydrochloric

acid" or "muriatic acid " or "spirits of salt" . of commerce The cold water in these WoulfrVs | bottles absorb? nearly 500 times its own bulk of : tin acid fumes, jind, when fully charged, contains about 40 per cent, of that acid. The same plant serves, after a thorough cleaving out, for the manufacture of nitric acid or spirits of vitro, usiug in this case saltpetre instead of common salt, and leading the acid fumes into Woulffe's bottles containing only a very small quantity of cold water. The equation for making muriatic acid is 2NTaCI + H,SO t = Na,SO 1 + 2HCI. which reads : 1171b i f palt heated with 981b of strong su'phuric acid will yield 1421b of salt cake and 731b of pure muriatic acid gas. This would make 1801b of the strong f umiDg muriatic acid cf commerce. For nitric aciJ the equation is 2KNO 3 + H a SO 4 = K 2 SO l -i- 2HNO E ; or, 2NaNO 3 + H.,SO l = Na 2 SO. t + 2HNO.,— 2021b of common saltpetre (KNO 3 ), or 1701b of Chili saltpetre (NaNO 3 ), yielding 1261b of pure fuming nitric acid. The visitors turned their attention next to the acetic acid plant in another part of the works. Here they saw the steam jacket surrounding and enclohiug the still or retort in which the strong fculphorie acid attacks the acetate of soda, driving out the acetic acid in the form of fumes, wbilc keeping the soda to itself. The equation is — 2NaC 2 H.,O 2 + H 2 «0 4 = 2C 2 H > 020 2 + Na 2 SO lf meaning that lG4lb of acetate of soda will require 981b of sulphuric acid to make 1201b of pure acetic acid, and leave in the retort a residue of 1421b of sulphate of soda. The arrangements aud Woulffe's bottles for condensing and collecting the acetic acid are quite similar to these described above for collecting the nitric acid. They next saw the whole prccess for make superphosphate of lime — tho soluble phosphate, of farmers. This manufacture is carried on in large, flatbottomed, oblong, wocden vats about, say, 12't long by 7ffc wide and 2ft deep. Into these vats I i 3 poured fiist a strong liquid nitrogenous I material extracted from bones aud other ! agnail matters ia another part of the works; over this is poured 10 or 12 i 3g-il j\rs cf the strong sulphuric acid already df scibed ; and then the bouedust, or guano, or ■ mixture ol both that is defined to be converted ! iuto superphosphate is delivered by barrowfuls and rapidly shovellod iuto the acid mixture and rabbled through the heavy liquid by longbandied, large wooden hoes. Immediately the ! mixture begins to effervesce and give forth clouds of stciru and carbonic acid gas. Very soon il becomes strongly heated by the chemical

I action of the acid ; more and more raw phosphates are shovelled into it. The heat increases, the fumes become intolerable, and a clear space is soon created around the seethiug, puffing, sweltering vats. In the course of half an hour or so, however, the chemical process is finished ; the feulphate of lime absorbs the spare moisture and the clouds clear away ; the cir resumes its normal condition of comparative purity ; tho vats are ready to be discharged, aud the superphospate is hurled away, to ripen in tho sheds and to await a purchaser. „ The guano and crushed bones before this sulphuric acid treatment contained their phosphate of limo in its insoluble or tricalcic state — Ca 3 P 2 O s . The sulphuric acid changed this into the soluble or monccilcic state, CaH,P 2 O q , and there was produced at tne same time in the vats a quantity of sulphate of lime — CaSO,, which contains sulphur and lime, both soluble ; so that now the superphosphate cont»ius threo soluble ingredients — namely phosphoric acid, lime, aud sulphur, all of whicrl are required as plant food. The action of the sulphuric acid on the insoluble phosphate of the guano or bones ia shown thm :—: — Ca,P.iO B + 2H 2 SO t = CaH^O, + 2CaSO lt which may bo translated thus :—3lolb: — 3101b of iuAolublo tricalcic phosphate acted on by 196 b of sulphuric acid will make 2341b of soluble or monocalcic phosphate and 272. b of sulphate of lime. It is the sulphate of limo par; of this manure that dries it up. It is desirable aUo that thare should be a little carbonate of lima in tho raw material so as to furnish enough carbouicacid gas in the vats to make the whole mass porous and loose in texture, like thesponginess of properly baked bread, whoso openness and lightness are due to the same cause — namoly, carbonic acid gas. The students were then invited into tho ammoni.i department, where they saw the boiler into which are put the sulphate of ammonia crystals and the slaked lime that is to expel the ) ammonia gas from that salt. The boiler is an iron one built into a firebrick furnace so that the flames may be equally distributed over the bottom of it. The mixture of lime and sulphate when heated gives off voluminous but invisible vapours of ammonia along with some steam. These hot vapours are led up into a metallic drum at the ceiling, where most of the steam is condensed to liquid water, whilst the ammonia gas travels on through the pipe that leads irom the drum , up through the roof, where it takes the form of a spiral coil or worm, which, being kept cold by the air, condenses the rest of tho water, leaving

the ammonia gas to pursue its way down through the descending pipe into cold water contained in a series of large Woulffe's bottles similar to those described for the manufacture of muriatic acid. The ammonia gas — NH, — dissolves in the cold water just as the muriatic acid gas docs, and the excess of ib passes from one Woniffe's bottle to the next till they are all charged and saturated with it.

The water absorbs about 1000 times its own volume of the gas, and, in doing so, becomes heated and expands till the specific gravity is •88. It is then ready for the market as "ammonia fortissima." The sulphate of ammonia used is got from the company's Auckland works, where it is made from the amaioniacal liquor of the gas works. The Newcastle ccal used at Auckland for gas making contains more nitrcgen than our West Coast coal, and that nitrogen appearo in the gas liqaor as aiinaonia iv such quantity that it can ba profitably extracted. The equation for getting ammonia from sulphate of ammonia is : (NH?) 2 SO J + CaOH 2 0 = CaSo l -!-2H0.,-h 2NH,, which reads 1321b of sulphate of ammonia, heated with 741b slaked lime, will produce 1361b sulphate of lime, 361b water, and 341b ammonia gas. A good deal of sulphate cf ammonia is used at these works for putting into the manures to raise their percentage of ammonia. This is a most commendable use to make of that salt, as in the state of sulphate the ammonia is not only ready-made, but readily soluble, so that the plants may have the immediate use of it. An outstanding feature of these chemical and manure works at Burnsido is the fact that since they make their own sulphuric acid for the manufacture of superphosphates they can very well be liberal in the use of that necessary material in their vats. Their position, adjacent to the freezing works and saleyardß also, is a most favourable one for getting large supplies of blood and bones and other animal matters rich in nitrogen for their manufacture. When the party had had their fill of the chemical and manure works they adjourned to the freezing works, and were heartily received by Mr Scott, the manager, who at once put them on a home footing in the large establishment under his charge. Their first experience ! there, however, was a very rold one, as Mr Scotfc, with a good deal of dry humour, insisted on putting them all, in two detachments, right through the freezers— ladies first. Being under his own (I cannot say genial in there) I guidance, howovcr, lantern in hand, with '. which several of them were also furnished to

help to guide them on their chilling way, thoy proceeded with some misgiving into Mr Scott's polar regions.

As they pursued their shivering way with sheep, dead and disembowelled, by the hundred hanging hard as iron on each side of them, with the crystalline snow inches deep, hard and glitteriDg in the candle light, clinging to the walls that narrowed their frozen path, with their very breath freezing into a lino whito mist of 3now at every exhalation, and with the iutimation (which they at first took for a grim joke) that after doing the whole long length of this arctic parade they must, in order to got back to the light of day, retraco their freezing footsteps and do it all over again, their state of mind as well as of body may bo imagined ;it cannot be described. They were haunted, too, by the benumbing dread that some of their number might wander in the darkness aud got left behind in these glacial regions. The first detachment (including all the ladies of thtf party) having emerged into the light arcl warmth of tho outer air, hurried the other.-, in a very encouraging way, into the cadaverous aud blood-curdling labyrinth of frost and snow from which they themselves had just escaped alive. Their safe return, after five minutes' experience of tha frozen horror, however, equalised matters, and the whole party were hurried round by Mr S^ottiuto the enginehous". to thaw; and thtro I hey saw the throbbing machinery at work compressing the air which by its ixpansion in the chamber is to produce tho searching cold that sends these carcdees across Iho equator to England safe from the touch of tho putrefaction fiend. Mr Scotb very clearly exfl-iiuod the wonderful way in which the heat is sq>°rzjd out of the air when, as here, a great volume is compressed into a small space ; and how, when this same air (vow cold) is allowed to resume it 3 original volume, it demands the native heat which had been squeezed out of it ; and, this having now been lost to it for over, it draws out of all surrounding objects (sheep, &<;.) the heat that properly balonga to them, aud thus reduces them to the frozen state in which they are seen in these frigid chambers.

Nothing could exceed the heartinjss with which both Mr Smith and Mr ScoU received the excursionists, took them through the works, and showed and explained to them everything as they went along. Before leaving the platform a very hearty cheer was accorded to both these gentlemen for the very instructive > and pleasant outing their courtesy had. afforded their visitors.

The visit concluded with an adjournment to Mrs Kecnan's, where ample provision had been made for the requirements of the inner man, which was duly acknowledged by a hearty vote of thanks accorded to the very able manageress that presides over that well-known house of entertainment.

The next lecture will treat of potash and soda in the soil, the crops, and manures.