208 Miscellaneous Tntelllgence. 



ultimately predominated : small quantities of other unimportant sub- 

 stances were formed. The pyrophorus obtained burnt well, evolving 

 much sulphurous acid, hence a poly-sulphuret of potassium must 

 have been produced. The excess of sulphur must have been de- 

 rived from the sulphuric acid of the sulphate of alumina, and evi- 

 dently from the latter portions only. Evidently no free potassium 

 can exist in the pyrophorus ; and the same fact is proved by the 

 action of water upon it, which produces no hydrogen. 



Charcoal is not necessary to the pyrophorus, for when only so 

 much was used as was sufficient to decompose the alum suffi- 

 ciently, without leaving any excess in the pyrophorus, still the lat- 

 ter burnt well, and left a grayish-white residue. Nor is the 

 alumine necessary ; for using an atom of sulphate of potash, and 

 3 of sulphate of magnesia, instead of alum, good pyrophorus was 

 produced. 



Considering that the alumina and the magnesia were merely 

 useful in dividing the sulphuret of potassium existing in pyropho- 

 rus, which is the essentially active ingredient, and that their places 

 might be filled by charcoal itself; a mixture of 1 atom of sulphate 

 of potash and 4 of lamp-black was made and heated ; only an aggluti- 

 nated sulphuret was obtained, which did not inflame in the air ; 

 but, doubling the proportion of charcoal *, a pyrophorus was 

 obtained, so combustible, as not to bear transferring without diffi- 

 culty and danger. 



Tliis pyrophorus produced no sulphurous acid during combus- 

 tion, but a neutral sulphate of potash ; dissolved in water it gave, 

 with acids, sulphuretted hydrogen, and a deposit of sulphur. Hence 

 it is not a single sulphuret of potassium, but a poly-sulphuret, 

 and, consequently, a part of the potassium is uncombined with sul- 

 phur. This potassium is not free, for no hydrogen is produced in 

 water, and therefore it must be combined with oxygen ; nor, 

 indeed, does the pyrophorus require a moist atmosphere, but burns 

 equally well in dry air. The charcoal does not appear to be in 

 combination either with sulphur or potassium, for the solution in 

 water does not differ from that of a sulphuret without charcoal ; 

 and the charcoal which falls to the bottom of the solution has not 

 that state of division which indicates an anterior state of combi- 

 nation. 



Sulphate of soda in equivalent proportions gave an equally 

 powerful pyrophorus, but sulphate of baryta did not. The new 

 pyrophorus owes its superiority over that ordinarily prepared, to its 

 more intimately divided state ; to the absence of inactive earthy 

 matter ; and the smaller proportion of sulphur. 



A high temperature did not improve this substance ; an ordinary 

 portable furnace was used, but great care was taken to prevent the 

 access of air during the cooling. — Ann. de Chimie, xxxvii. 415. 



• By weight about 1 of lamp-black and 2 of the sulphate of potash. 



