NITRATES FROM THE AIR.

Otago Witness, Issue 2715, 28 March 1906, Page 7

NITRATES FROM THE AIR.

The Friday evening discourse at the Royal Institution on February 2 was of exceptional interest, as Professor Silvanus Thompson gave a demonstration of the method that is being used 'in Norway for the manufacture of nitrates from the air. The professor began by a reference to tl c remarkable paper by Sir Will jam Crookes before- the British Association in 1898, m which it wae conclusively proved that in a comparatively small number of years (about thirty) all the available space in the world would be given over to wheat cultivation, and that thereafter, unless the land can be made to produce more wheat per acre, the inhabitants of the globe will suffer from a shortage of the wheat supply. The population is growing' at a greater rate than the increase in the wheat-growing area, and although new fields are being cultivated the average acreage devoted to wheat is decreasing. In a few years the United States will have to import wheat. The only chance of averting famine is to increase the yield per acre by means of special manures. Wheat requires fixed nitrogen as a fertiliser, and this ie supplied by natural manures, sulphate of ammonia, and nitrate of soda. Natural manures, such as guano, are practically exhausted, while no great increase can be expected in the production of sulphate of ammonia. There remain, the nitrate of 6oda deposits of Chili, hut these at the present yearly Tate of consumption (l£ million tons) will be exhausted in fifty years. As larger quantities are used each year, the exhaustion of the Chili saltpetre beds niay be expected long before them. The yield of wheat per acre varies from 41.8 bushels in Denmark to seven bushels in South Australia, the figure for the United Kingdom being 29.1 bushels. In 1931 all the. lamd will be in use, and it will be necessary to grow more wheat per acre. Starvation may be averted through the laboratory by the discovery of a sufficiently cheap method of fixing the nitrogen of the air co that it can be ussd as. a wheat fertiliser. To give an idea of the enormous amount of nitrogen in the air, Professor Thompson said that in that lecture theatre there was four tons of nitrogen, which, if combined with soda, could be sold for £240. Cavendish 6ome 120 jears ago showed that nitrogen aa,d

oxygen can be combined by passing electric sparks through tho air; and Davy, in that very theatre, first showed the electric wire by which the combination can. be brought about. These early experiments were followed by years of patient investigation by Dewar, Orookes, and Rayleigh, the lastnamed declaring that if electricity could be had at one-seventeenth of a penny per unit nitrate of soda, could be manufactured at £5 a ton. Sir William Crookes's prophecy that the fixation of nitrogen in quantity would be possible is now fulfilled, as nitrates are actually being produced from the air in quantity. In Scotland electrically manufactured cyanide is being made at the rate of 20 tons a -week, and in Berlin eyanamide is being made, but only in experimental quantities. Other experiments in the fixation of nitrogen are being made in the United States, at Geneva, and at Freiburg. One difficulty in the electric fixation of nitrogen is that the yield of oxidised nitrogen obtained from air by the electric discharge is very small ; the reaction is reversible, and the nitrogen oxides formed are in torn split up by the epark into free oxygen and nitrogen as soon &3 they are present in any quantity. But if the operation is conducted at a high temperature a considerably larger percentage of oxides has to be present before this reversed action takes place, and, further, the formation of those oxides is rendered more rapid. These facts are utilised in the process of Birkeiand and Eyde, of Christiania. who make use of a special electric furnace. In this an alternating electric arc is produced at between 3000 and 4000 volts, and 'is formed between the poles of an electro-magnet which forces it to take the shape of a disc of roaring flame, 4ft or sft in diameter. Ordinary air is blown through the furnace, and emerges charged with nitrous fumes, the rapidity with which the product is removed from the sphere of operations being an important •element. The nitrous fumes are collected, allowed time- to oxidise still further, and thon absorbed in water-towers or in quicklime. Experiment shows that the- nitrate of lime produced is as good a fertiliser as Chili saltpetre. The conditions in Norway aro exceptionally good for furnishing cheap electric power ; the cost at the factory now in operation at Notodden it less than one-tenth of a penny per unit, and when further extensions have been carried out it is expected it will be reduced to about one-fortieth of a penny Hence the new "' Norwegian saltpetre " will be ab!e to compete with the imported saltpetre from Chili, and will every year become more valuable as the demand for 'nitrates increases and the natural supplies become exhausted.

Mr Eyde, an electrical engineer and partner with Professor Birkeiand, was present, and tinder his direction s model of tho furnace in use at Notodden was shown in operation. The model apparatus was devoid of the outer cover, and orn-e could see a broad circle of flame Bin across in which was concentrated 50 liorse-power. The apparatus made a fearful noise while it was working. Professor Thompson showed a number of slides illustrating the apparatus used at the Norwegian works. The suggestion to form basic nitrate of lime is due to I>r Messel. It has been tried by the Norwegian Agricultural College, and found to answer perfectly as a fertiliser in place of Chili saltpetre. The calcium nitrate is fused and poured into large iron drums for eale. Samples of the products were shown at the meeting.