Biography of Berzelius. 11 



prised the compounds of chlorine, bromine, iodine, fluorine, 

 and cyanogen, as well as other compound radicals with 

 metals. 



This discovery of sulphur salts is indisputably one of the 

 most important extensions of chemistry. Berzelius entered 

 upon their study with great industry, and the number of sul- 

 phur salts examined by him amounted to about 120, to many 

 of which he certainly could only give a passing attention, 

 although he analyzed many quantitatively. 



Next to this followed his investigation of hydrofluoric 

 acid, one of the most important which Berzelius executed, 

 since it has thrown such an unexpected light upon several 

 of the most interesting departments of chemistry. 



Thenard and Gay-Lussac had indeed already prepared 

 hydrofluoric acid in a pure state, and several of its com- 

 pounds. But as they were at the same time occupied with 

 a number of other important researches, they did not pur- 

 sue this subject further, and especially did not study with 

 sufficient accuracy the phenomena which presented them- 

 selves when potassium was heated in fluoride of silicium. 



Berzelius, in the first instance, prepared the most impor- 

 tant metallic fluorides ; then he went on to the remarkable 

 compounds which hydrofluoric acid forms with electro-ne- 

 gative fluorides, especially fluoride of silicium, and fluoride 

 of boron, but also with fluoride of titanium and others. It 

 was through him that we first acquired a correct conception 

 of the composition of hydrofluosilicic acid and the fluosilicates, 

 as well as of the action of water upon fluoride of silicium. 

 But the most productive part of this investigation was when 

 Berzelius repeated the experiments of Gay-Lussac and 

 Thenard, for the purpose of decomposing fluoride of silicium 

 by means of potassium. He had just at this time learned 

 from Wohler how to prepare potassium by means of car- 

 bonate of potash and carbon according to Brunner's method, 

 and thus provided himself with large quantities of this 

 metal. On decomposing fluoride of silicium by potassium he 

 obtained the same results as the French chemists, namely, the 

 brown non -metallic substance which they regarded as a com- 

 plex compound of fluosilicide of potassium and of fluoride of 



