332 On some Comlinaiions of Platinum. 



after some time it acquires fulminating proijerties. The quan-. 

 tity of air I have hitherto obtained in this way, has been too 

 small to allow me to ascertain its nature with precision. When 

 the powder is brought in contact with ammoniacal gas, a crack- 

 ling noise is produced, and it becomes red hot and scintillates ; 

 but bv this treatment its external appearance is scarcely altered, 

 though it undergoes a partial decomposition. The powder is 

 immediately decomposed bv the agency of alcohol. This fact is 

 shown in an interesting manner by moistening different sub- 

 stances, such as paper, sand, cork, &c. with alcohol, and placing 

 the smallest particle of the powder on them ; it hisses, a suffi- 

 cient degree of heat is produced to reduce and ignite the pla- 

 tinum, and it remains in a state of ignition until the alcohol is 

 consumed. During the agency of alcohol on the powder, acetic 

 acid is produced. This is shown by putting a little of the pow- 

 der on a paper filter and moistening it with alcohol ; a moderate 

 action takes place, and in a {ew minutes the odour of acetic 

 acid is very perceptible. In some experiments of this kind, the 

 action, though comparatively feeble at first, has presently in- 

 creased, the powder has become red hot, and the bottom of the 

 filter completely cliarred. If two or three grains of the powder 

 are placed in a glass, and a few drops of alcohol added, in about 

 half an hour acetic acid will be produced ; and as it evaporates 

 and disappears, it may be successively renewed, at longer or 

 shorter intervals, for some weeks, by occasionally adding a little 

 alcohol. 



When the powder is boiled in alcohol, it is partially decom- 

 posed, and assumes a lighter colour ; if it be then thrown on a 

 filter, the odour of acetic acid is soon perceived, and in a few 

 hours the jjlatinum is found i-educed and the paper charred. 

 When the powder is mixed with flowers of sulphur, and heated, 

 a sulphuret of platinum is formed of a blue colour. When the 

 powder is heated with phospiiorus, there is a brilliant combus- 

 tion, antl a dark-grey phosphoret is formed. Oxygen gas does 

 not affect the powder at the common temperature of the air ; but 

 bv a moderate heat there is a slight combustion, which seems to 

 indicate the presence of a little inflammable matter. 



3. Composition of (he peadiar Compound. 



In my first attempts to ascertain the nature of the black pow- 

 der, I was limited to very minute (juantities of it; and I made 

 several trials before I gained any satisfactory evidences of its 

 constitution. I decomposed the powder in long g.'-een glass tubes 

 filled with mercury ; in such cases, by a gentle heat, the powder 

 became ignited, the reduced platinum awialgainated with th« 

 mercury, a little fluid appeared, and some gas wa« evolved. The 



fluid 



