on Emetic Tartar, and on a new Ptjrophorus. 189 



I found that 100 parts were composed of 



Protoxide of antimony 42*6 



Tartaric acid 45*0 



Potassa 9-8 



Water 5-75 



101-15 

 If we reckon tliese parts according to the laws of atomic 

 combination, we find pretty nearly that emetic tartar may be 

 considered as a compound of one proportion of sub-tartrate 

 of protoxide of antimony, with half a proportion of neutral 

 tartrate of potassa ; and tliat one atomic proportion of it must 

 be expressed by the number 231*7. For 



Two proportions of protoxide of antimony =2x 48=960 \ ^"^ P''°P" °^ p 



One proportion of tartaric acid 69-8 j P^^^rtrate ot 



( antimony. 



Half a proportion of potassa 22'5 S Half a prop, of 



Halt a proportion of tartaric acid 34-9 



One proportion of water 8-5 



neutral tartrate 

 of potassa. 



231-7 

 100 parts of this compound then consist of 



Protoxide of antimony 41*4 



Potassa 9-7 



Tartaric acid 45-1 



Water 3-6 



99-8 

 which agrees very nearly with the experimental result. 



C. A 7ieuo Pyrophorus. 



While I was determining the proportions of the component 

 parts of the tartrate of lead, I found that when it was heated 

 in a glass tube, it produced a most beautifid pyrophorus. 



When a portion of the dark-brown mass is shaken out of 

 the tube, it catches fire immediately, and there appear on the 

 surface of the ignited body, brilliant globules of lead, some of 

 which become gradually changed into the yellow oxide, afFord- 

 inga most interesting spectacle. 



The brilliancy continues much longer than in other pyro- 

 phori, so that, on account of its easy preparation, this might 

 afford a convenient method of producing fire. 



The inflanmiation of such pyrophoric substances has of late 

 been attributed principally to potassium ; but this pyrophorus 

 gives us a new proof that other metallic comjjounds (as in this 

 case the carburet of lead ?) are susceptible of spontaneous in- 

 flammation on coming into contact with the air. 



XXXVIII. True 



