310 Biography of Berzelius. 
In the former paper Berzelius had directed attention to the 
compounds. 
The different sulphur compounds of the electro-negative met- 
als which Berzelius called sulphids, and whose composition is 
analogous to that of the metallic acids, combine with the electro- 
positive or basic sulphurets in such proportions, that if the sul- 
phur were replaced by an equal number of atoms of oxygen, 
some one of the salts would be formed which the same radicals 
would yield in their oxydized state. 
the sulphur compounds of the non-metallic elements, those 
of carbon and hydrogen alone combine with the basic sulphurets 
of the metals; the latter class of compounds,—those of sulphuret- 
ted hydrogen with alkaline sulphurets,—were already known un- 
der the name of hydrothio-alkalies, but their true composition 
Was not recognized until now. 
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 sulphur salts ex- 
amined by him amounted to about 120, to many of which he cer- 
tainly could give only 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 inter- 
esting departments of chemistry. ae 
_ Thénard and Gay-Lussac had indeed already prepared hydro- 
fluoric acid in a pure state, and several of its compounds. But as 
they were at the same time occupied with a number of other 
