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BAD AIR AND GUX COTTON. At the request of the Royal Commission which has recently reported on the condition of the Cornish and other metalliferous mines, Dr. Angus Smith examined the quality of the air which the miners have to breathe, to the impurity of which is chiefly attributable the early break down in their strength. A healthy atmos- phere may be taken to be one with 20 9 per cent of oxygen, and 0-1)4 per cent. of carbonic acid gas. Late in the evening in the pit of London minor theatres as much as 0-252 and 0-320 percent, of carbonic acid has been found; but the average of above 300 samples of air taken from these milles had 0 785. Two thirds of the samples presented an atmosphere exceedingly bad, and the worst parts of the mines had only about 18-69 per cent. of oxygen, and as much as 1-8 or more of car- bonic acid, in one instance 2-26 per cent. In order to test the effects of such bad air Dr. Angus Smith caused to be constructed a small close chamber of lead, with windows sufficiently large that they might in any emergency be broken through for a way of escape. The explosion of gunpowder produce sulphide of potassium, the effect of which is probably like that of sulphide of hydrogeu, but from its acting more slowly there is dis- tributed over a long period that death which might ensne instantly, and so, in chymical phrase, the effect is dissolved in health, and becomes disease. Gun cotton seems to promise to perform the work of blasting with less injurious influence upon the air. Mr. Hadow, F.C.S., in his chemical Report slates I have care- fully examined the sample of Gun-cotton rope, and am able to report favourably upon it. Gun-cotton proves on analysis to be the highest and most powerful explosive of the series of substitution compounds formed by ihe ndon of nitric acid on cotton. The fact of its containing the maximum amount of peroxide of nitrogen was proved by submitting a portion, carefully dried in vacuo, to the reducing action of an alcoholic solution of the double sulphide of potassium and hydrogen, when it ga.'e an amount of cotton almost exactly corresponding to that which calculation requires (100 parts gave 54'80, cal- culation requires 64.51 of cotton); and secondly, by treating another portion, likewiie weighed after drying in vacuo, with a mixture of the strongest nitric and Bulphuric acids for three hours, when the presence of any of the lower substitution compounds would have been detected by an increase of weight after washing and drying (the next lower substitution compound gaining ,)'3, and the next lower 11'3 per cent, by such treatment.) The sample, however, gained nothing in weight by the immersion; on the contrary, as experience has proved to be the case with Gun-cotton that has reached the highest stage of substitution, a loss was sustained of O',) per cent., which corresponds very closely with what experiment shews to be the loss sus- tained always through solution, by immersion of the strongest Gun-cotton for three hours in the mixed acids, "Your Gun-cotton possesses a high degree of stability, and of all the samples I have examined it is the least likely to change during prolonged storing. "The sample was found perfectly free from all un- combined: acids,—it had in fact a vcry feeblo alkaline reaction (due to silicate of Ðodl), only discoverable by testiug with care. In the preceding statement as to the amount of cotton obtainable from the Oun-cotton, and as to the weight after immersion in acids, the amount of ash and soluble matter was ascertained both before and after treatmeutj aud waa deducted iu the calculations."