*6S 



APfARATUS FOR TRUSSIAN BLWE. 



many otlier occasions) could never detect the smallest trace of 

 arsenic in it. 



{To le concluded in our next.) 



IV. 



Description of an Apparatus by means of which all had Smell 

 may be avoided in manufacturing Prussian Blue : by Mr. 

 d'Akcet*. 



Manufacture 

 of Prussian 

 blue ofFensive, 

 One source ob- 

 viated. 



Another from 

 the potash. 



Apparatus to 

 obviate this. 



Dascribed. 



THE manufactures of Prussian blue diffuse to a distance 

 two kinds of bad smell. The first, that produced from the 

 combustion of animal matter, is easily avoided by covering the 

 crucible with a dome, at the summit of which is the chimney 

 of the furnace, and setting fire to the vapours emitted from the 

 crucible, as soon as they are hot enough to burn. 



The second source of the bad smell is found in the use of 

 the potash of the shops, which contains more or less sulphate 

 of potash. When the mixture of blood and potash is calcined, 

 the temperature is high enough for the sulphate to be decom- 

 posed and converted into sulphuret, by means of the animal 

 charcoal mingled with it : whence it follows, that the Prussia 

 liquid always contains hydrosulphuret of potash in solution j 

 and that, when this liquor is mixed with the solution of alum 

 and sulphate of iron, a large quantity of sulphuretted hidro- 

 gen gas is evolved, which is extremely fetid, and diffuses itself 

 to a distance, tarnishing plate and spoiling meat, that is within 

 its sphere of action. 



By means of the apparatus about to be described, these in- 

 conveniences may be avoided, and the sulphuretted hidrogen 

 gas evolved on the mixture of the two liquids may even be 

 turned to advantage. 



PI. VII, fig, 1, a, is a tub of white wood, well hooped, and 

 firmly supported by two pieces of wood, that raise it from the 

 ground, and preserve the bottom from rotting. 



i is a hemisphere of thin copper, of the same diameter as 

 the tub, and serving as a cover to it. It fits into it up to the 



* Ann.de Chim. vol. LXXXH, p. 165. 



