Art. XXVIII.—On the effects of the Application of the Hot Blast to Blow-pipe purposes: and the proposed substitution of Heated Air for Oxygen in the production of certain thermal and illuminating effects. Preliminary notice.

Transactions and Proceedings of the Royal Society of New Zealand, Volume 2, 1869, Page 148

Art. XXVIII.—On the effects of the Application of the Hot Blast to Blow-pipe purposes: and the proposed substitution of Heated Air for Oxygen in the production of certain thermal and illuminating effects. Preliminary notice. By W. Skey, Analyst to the Geological Survey of New Zealand. [Read before the Wellington Philosophical Society, June 19, 1869.] The useful and well-known effects of the hot blast, in the process of iron smelting, has induced me to try and extent it profitably to other purposes, beyond that which prompted its application in the present instance. My experiments, as yet, have been confined to testing the effects of substituting a hot blast, for a cold one, as hitherto used, for the production of the well-known blowpipe flame; a flame so produced will be expected to have its thermal and illuminating effects augmented, but scarcely, perhaps, to that degree which experiment has demonstrated. I had better state, at the outset, those particulars which it is necessary to know, before relating the results. The temperature of the blast was, approximately, 500o F., the diameter of the jet, regulating its issue, was one-thirtieth of an inch, the combustible for receiving the blast was stearine. This flame manifested a very marked superiority over the common blowpipe flame,—substances difficult to fuse in the latter, magnitite, potash-felspar, mica, readily yielded under these circumstances; while thick glass tubes half an inch in diameter, and hard German glass tubes, were tractable to an eminent degree. Carrying my test experiments still further, I found several substances, for the fusion of which the oxy-hydrogen flame, or some equivalent of it in heating power, is said to be indispensable, also yielded before the blowpipe flame thus urged: for instance, platinum, pipe clay, fire clay, agate, opal, flint. Several samples of each were tried and always with the same results, it could not well be, therefore, that the fusibility of any of these substances was due to the accidental presence of foreign matter, in more than usual quantity. The platinum was the common platinum foil, also a sample prepared especially for the purpose; the only impurity found in it was iron, as traces, communicated to it in the act of forging: possibly minute quantities of some

of the other metals, of the platinum series, might be present, but they would rather tend to increase its infusibility than otherwise. Alumina only appeared to vitrify; while, after numerous trials with crystallized quartz, I could not succeed in fusing it to a globule; thin splinters however curled round upon themselves, like scolezite, and ultimately assumed a glazed appearance, clearly showing that the melting point was all but reached. It appears from this that a very small amount of some foreign substances exercises a marked effect upon the fusibility of silica, agate, opal, etc., being only a little less pure than rock crystal, though so readily fusible in this flame. Regarding the illuminating power of the flame so produced: when allowed to impinge upon a solid substance such as lime or magnesia, it was not only more intense (as would be expected), but the volume of incandescent matter was largely increased. Before I proceed to urge the further use of hot air for combustions where high temperatures are necessary, I wish to call attention to the fact, that the temperature of the flame, which I have hitherto worked with, can be largely and economically increased, by increasing that of the blast; this can easily be done to a threefold extent. By substituting heated hydrogen (or burnt coal gas), I have also realized all the effects just instanced, with greater rapidity and decision; but the great diffusiveness of this gas, especially when heated, has prevented me as yet carrying the experiments further. While on the subject of heating both combustibles (at least both the substances which take part in these combustions), I cannot refrain from remarking how easily the temperature of the oxy-hydrogen flame even, could be increased in this manner—the gases would of course have to be heated prior to contact. Upon their more vigorous diffusiveness, when rarified, I should rely for that solidity of flame, so necessary where the communication of very high temperature is desired. The jets regulating the issue of the gases would have to be very fine. Proceeding now to the next part of this subject: the result of these experiments, instanced, urge me to recommend, for trial, the substitution of heated air for oxygen, in most of those cases where this gas is now employed in conjunction with hydrogen, or other combustible matter, as a generator of heat or light: for instance,— 1. In the metallurgy of platinum, that part of it where the metal has to be fused; also in soldering platinum stills for sulphuric acid works. 2. The fusion of alumina in the manufacture of certain gems. 3. In the production of the Drummond and Bude lights. The fusion of platinum and alumina is now effected by the oxy-hydrogen flame. Relative to the competency of heated air to perform the part of cold oxygen in the production of such intense lights as these (the Drummond and the Bude), I think this can be demonstrated, almost to a certainty, in the following way: Thus—the flame employed in these investigations has certainly a minimum temperature of 4596o F., since this is the fusing point of platinum, the substance most easily fused of all those I have tried, that are infusible in the common flame; doubtless the temperature is considerably higher, but I will take these figures. On the other hand, the actual temperature of the lime, when the Drummond light is in operation, is (on the authority of Tyndal) only 2000o Cent.=3632o F.; hence this flame has an excess of temperature over that of the incandescent lime, equal to 964°F., a pretty good margin for

loss, surely sufficient if properly economised; but as I have already shown, this excess of temperature can be largely increased. In view of the greater controllability of the proposed substitute,—the absence of all danger in its use—its not requiring chemical preparation,—and its cheapness, compared with oxygen; upon these several points, respectively, the question should be properly tested. Besides the substitution of oxygen urged above, the possible fusion of the purer clays, and certain silicas, etc., in a ready and economical manner, may induce the further utilization of these substances, while in experimental chemistry the facility with which such high temperatures can be attained and kept up, may lead among other things, to some cheaper way of extracting certain metals from their oxides, aluminium, for instance, from alumina or clay. On reviewing these results, it does seem not a little singular that a difference of not more than 500o F., in the temperature of the blast, should make the difference between the fusibility and infusibility, of such substances as platina, agate, fire clay, etc., in the blowpipe flame. It will be recollected, however, that the blast has, in this case, not only taken up the heat required to raise a single volume of it to this temperature, but another portion of heat has been taken up in a latent form, as the air expanded,—consumed as it were in lifting against the atmospheric pressure; this may be represented sufficiently well for us, by assuming the temperature of the blast, kept to its normal volume, at 700°F. This is as yet, however, but a very slight addition of produce results, which so nearly approximate to those obtainable by the oxy-hydrogen flame, seeing the latter has an estimated temperature of 14,000° to 15,000°F., while that of the present method does not much exceed 5,000°F. The gap, as far as effects is concerned, is narrowed so much, and in a manner so unexpected, by the results here given, that one is naturally prompted to enquire whether the assigned temperature of the oxy-hydrogen flame has been obtained by direct experiment, or by calculations, based upon the ascertained temperature of other flames. The temperature as calculated, indirectly, in this last way, certainly furnishes us with figures remarkably close to those just quoted. In reference to this important point I beg to call attention to a notice, which appeared in the “Chemical News,” relative to the imperfect combustion of certain gases at high temperatures. There we learn that at moderately high temperatures (much below 10,000°F.) oxygen and hydrogen only very partially combine,—from memory, I believe, not more than to the extent of half their weight,—the remainder of the gases of course combine, as the centre of heat is left behind. Thus, although the quantity of heat evolved by their combustion is the same, being divided over a larger volume, its intensity is proportionately diminished. This being so, it would seem to follow, that the temperature of the oxy-hydrogen flame must be very considerably lower than that hitherto ascribed to it; and therefore the possibility of substituting it in this, or in some other manner equally economical, for the several purposes here specified, appears so much the greater.