£58 HISTORY OF PRUSSIATES. 



solution of red oxide, without the assistance of black oxide. 

 Hence the risk of losing all the simple prussiate contained in 

 A lixivium, if we were to use only a sulphate, the oxide of 

 which is completely red ; though this I formerly recommended, 

 The blue from but it was from mistake. I was not aware, that, if the green 



the green sul- su lphate have the inconvenience of aifording a pale prussian 

 phate is pale at ", ' ' . 1 . 1 . 



first, but grows blue, tne oxigen of the atmosphere soon remedies this ; and 

 deeper by ex- that j,t ] ias the essential advantage of furnishing the simple 

 ajj.^ prussiate with that portion of black oxide, which is necessary 



to convert it into a triple salt, and enable it afterward to 

 produce blue with the red oxide. Thus practice had at- 

 tained the object before theory : but practice in turn be- 

 comes a rational process, as soon as theory comes to its jus- 

 tification. Two other experiments will corroborate this. 

 Alum employ- The lixiviums are commonly precipitated by a solution of 

 ed > four parts of alum, and one of the sulphate of iron of the 



shops, 

 but it has no I divided one of these solutions into two parts. One was 

 chemical effect superox i c l ec l by the oxigenized muriatic acid, the other was 

 m the process. l J _ , ' , -it t 



not. I afterward saturated them with the carbonaceous re- 

 siduum. The common solution afforded abundance of blue, 

 but the superoxided yielded only a pale precipitate, which 

 was nothing but a little blue diffused among a great deal of 

 alumine. This experiment does not differ at bottom from 

 the preceding : it has only the advantage of showing, that 

 alum is merely a passive ingredient in forming prussian 

 blue. 

 The lixivium The lixiviums of the manufacturer, therefore, are not like 

 from blood not those made by treating prussian blue with an alkali. The 

 Hme^Ithlt latter will always afford abundance of blue, because it is 

 from prusssan mac [e a triple salt in the operation itself: but this is not the 

 case with the former; they afford blue only in proportion to 

 the quantity of triple salt they contain, and to augment this, 

 or to convert their simple prussiate into it, it is indispensable 

 to employ a sulphate, that, if not strictly green, at least 

 is so in a certain degree; and this is precisely the ease 

 with the sulphate, of the shops, however long it has been 

 mode. 

 In the calcina- From these details we learn farther, that, if the lixiviums 

 ti<,n of the contain but a certain portion of triple prussiate, it is either 

 blood probably because 



