376 Proceedings of Philosophical Societies. [May, 



very plainly that he does not consider the theory of Sir H. Davy 

 as being demonstrated. 



Selenium is excessively rare ; 500 lbs. of sulphur, when 

 burned in the manufactory of Fahlun, yields only one-third of a 

 gramme. In how much smaller proportion then must it be in the 

 pyrites from which the sulphur is extracted ! Prof. Berzelius has 

 since found it forming about the one-fourth part of an extremely 

 rare ore of silver and copper, extracted from a mine now aban- 

 doned in the province of Smoland, in Sweden, which he had 

 considered, on account of its smell, as an ore of tellurium. He 

 has also found some specimens of it combined with copper 

 without any silver. 



The more we reflect on these chemical elements, which appear 

 to be scattered at random by nature in such minute quantities, 

 that the most delicate exertions of art, and the most profound 

 science, are required to discover them, the more we are led to 

 believe that still more profound researches will hereafter strip them 

 of their rank of elements. 



M. Gay-Lussac made some researches in 1811 upon the 

 colouring principle of prussian blue, or that substance which has 

 been called for some time the prussic acid. These researches 

 showed that this substance, in a state of purity, had very remark- 

 able properties, of which we were until then entirely ignorant ; 

 such as, among others, the very small interval between its freez- 

 ing point and that of its evaporation, and its dreadful power upon 

 the animal economy. This experienced chemist, continuing his 

 researches upon this important subject, discovered in 1814 that 

 this principle was a hydro-acid ; that is to say, one of those sub- 

 stances which resemble acids in their action upon other bodies, 

 but in which the presence of oxygen could not be demonstrated, 

 and which appear to be formed by the combination of hydrogen 

 with a radical. The prussic acid is really the first hydro-acid 

 whose radical is known in respect to its elements, as M. Gay- 

 Lussac found that it was composed of carbon and azote in slightly 

 different proportions. He called the radical cyanogen, and the 

 acid produced from it hydrocyanic acid, on account of its 

 property of giving a blue colour to oxide of iron. We announced 

 all these discoveries in our Analyses for 1811 and 1814. 



M. Vauquelin has turned his attention to this subject, follow- 

 ing, as, with his accustomed modestv, he expresses himself, the 

 road which M. Gay-Lussac had marked out for him : neverthe- 

 less this road had some branches which could not escape a man 

 like M. Vauquehn. 



Gaseous cyanogen is absorbed by about four times and a 

 half its bulk of water, and communicates a very sharp taste and 

 smell to it, but without colouring it. This solution, in the course 

 of some days, becomes yeliow, and afterwards brown ; it depo- 

 sits a brown matter, acquires the odour of hydrocyanic acid, and 

 on the addition of potash, ammonia is developed. Nevertheless 



