18 18. J Triple Prussiate of Potash. 10'3 



to the base ; the two others much more obscure, and parallel to 

 two contiguous sides of the pyramids, or to two of the bevelled 

 edges of the tables. 



When exposed to heat, it gives out moisture, and assumes a 

 white colour ; but it does not melt, nor do the crystals lose their 

 shape, unless the heat approaches to redness. In a red heat, 

 the salt becomes black and alkaline ; but I was not able to 

 destroy its acid completely, even by long exposure to a red heat 

 in a platinum crucible. The solution of it in water, though very 

 alkaline, still continued to strike a blue with solutions of iron. 

 Its solubility in distilled water at different temperatures is as 

 follows : 



At 54°, 100 parts of water dissolve 27-8 of the salt. 



100 65-8 



150 87-6 



200 90-6 



The solubility does not seem to increase much by any aug- 

 mentation of temperature which I was able to try beyond 200°. 



It is insoluble in alcohol. My mode of determining the 

 solubility of salts in water and alcohol is as follows : I put a 

 certain volume of water or alcohol into a graduated tube, and 

 suspend a crystal in the tube. If the crystal be soluble, a current 

 of liquid may be perceived running down from the crystal to the 

 bottom of the tube. If it be insoluble, no such current is visible. 



2. When the salt in the state of a fine powder is mixed with 

 sulphuric acid of the specific gravity 1-844, it becomes imme- 

 diately very white, owing to the acid abstracting its water of 

 crystallization. In a few minutes a considerable heat is evolved, 

 and the salt begins to dissolve. If we apply the heat of a lamp, 

 a strong effervescence takes place, and gas is extricated in 

 abundance. At the same time the upper surface of the mixture 

 becomes dark blue, owing to the formation of a portion of 

 prussian blue. If the gas be received over mercury, a blue 

 liquid is soon deposited, consisting of water strongly impreg- 

 nated with sulphuric acid, and mixed, or rather thickened with 

 prussian blue. The gas thus received contains a mixture of 

 sulphurous acid gas ; but it consists chiefly of a colourless gas 

 having a peculiar smell, not sensibly absorbed by water, and 

 burning very readily with a deep blue flame. From 50 grains of 

 triple prussiate, and a drachm measure of sulphuric acid, I 

 obtained 36 cubic inches of this gas, and the evolution did not 

 stop till the mixture in the retort had become quite dry. 



This gas may be obtained in great purity by receiving it in 

 glass jars inverted on the water trough. Two hundred grains of 

 the salt mixed with four drachm measures of sulphuric acid will 

 furnish a quantity of gas amply sufficient to determine all its 

 properties. When the dry mass in the retort is dissolved in 

 water and filtered, 25*8 grains of prussian blue remain on the 



