298 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



and artificial carbonate of copper and that " in art as in nature 

 copper never oxidises beyond 26%," whether the oxidation 

 was brought about by fire, or by dissolving in nitric acid or 

 by conversion into verdigris. Thus, in reference to the native 

 carbonate of copper, he writes : 



" If 100 parts of this carbonate, dissolved in nitric acid 

 and thrown down by alkaline carbonates, give us 100 parts of 

 artificial carbonate ; if the base of these two compounds is 

 the black oxide, one must recognise an invisible hand which 

 holds the balance in the formation of compounds and 

 fashions their attributes at its will ; one must conclude that 

 nature does not act otherwise in the depths of the earth, than 

 on its surface, or in the hands of man " (Ann. de Chimie, 

 1799, 32, 30). 



In the case of iron and sulphur, Proust found an apparent 

 exception to his rule ; iron pyrites was not identical with the 

 artificial sulphide of iron (p. 175), but was " surcharged 

 with an excess of sulphur," about 20% of which could be 

 driven off by heating the mineral in a retort (Nicholson's 

 Journal, 1802, 1, in; tr. homjourn. de Physique, 1801, 

 53, 89-97). But in the course of the year 1802 he pre- 

 pared an artificial sulphide, which appeared to have the 

 same composition as iron pyrites, and concluded that 

 iron and sulphur could combine in two fixed proportions. 



" From the foregoing facts it follows, that iron can fix 

 sixty per cent, of sulphur by a considerably elevated tem- 

 perature. This proportion constitutes iron sulphurated to 

 the minimum." 



" By a lower heat it can also attract a [further] quantity 

 which is equal to half of this weight ; and this result is iron 

 sulphurated to the maximum, or with ninety parts of sul- 

 phur. If this last combination be exposed to the temper- 

 ature which formed the first, it returns to that state ; that is 

 to say, it returns to the minimum of sulphuration, by giving 

 out all the sulphur it was capable of fixing above the pro- 

 portion of sixty parts for each quintal of iron " (Nicholson's 



