1818.] Triple Prussiate of Potash. 109 



This tube is plunged into the mercurial trough; and the gas 

 extricated during the application of the heat is collected in glass 

 jars. The bulk of this gas being ascertained, a quantity of 

 caustic potash is let up into it. This absorbs the carbonic acid 

 gas. The residual gas in the present case, is azote. The increase 

 of weight in the muriate of lime gives the quantity of water 

 evolved. In making this experiment, easy as it may seem, 

 some precautions are to be taken in order to ensure accuracy. 

 I found that the results did not correspond well with each other, 

 unless the peroxide of copper be at least 20 times the weight of 

 the triple salt. I usually mixed 120 grains of peroxide of 

 copper with five grains of the triple salt. The salt was in its 

 usual crystallized state. I reduced it to a fine powder, and 

 mixed it intimately with the peroxide of copper. Glass tubes 

 are liable to melt if the heat employed be a little too great. I 

 found experiments made with them rather tedious and uncertain. 

 I, therefore, got a solid copper rod of the requisite diameter 

 bored into a tube. It was a foot long. The mixture of peroxide 

 of copper and triple salt filled six inches of it. The remaining 

 six inches I filled with peroxide of copper. To keep the per- 

 oxide from being driven out of the tube, or mixing with the 

 muriate of lime in the glass tube, I filled up the end of the 

 copper tube with amianthus. To the extremity of the copper 

 tube was luted with fat lute a glass tube, 

 bent as in the margin. That portion of it 

 which is marked with dots was filled with 

 dry powdered muriate of lime. The whole 

 upper part of it and the lower extremity 

 was filled with amianthus. After being 

 accurately weighed, it was luted to the 

 copper tube. The copper tube was placed 

 in a small chauffer, and so poised that about 

 eight inches of it were within the chauffer, the remaining four 

 inches were without. This exteriorportion was covered with a thick 

 coating of wet clay in order to keep it cool. The chauffer was 

 then filled with charcoal, and a sufficient fire raised to heat the 

 copper tube to redness. The portion of the tube without the 

 chauffer was screened from the heat. Its temperature became 

 somewhat higher than 2i2°, but not sufficiently so to alter the 

 lute, which i found after the process just as entire as at first. 

 I found it requisite to leave a portion of the glass tube empty of 

 muriate of lime ; because when that salt filled the whole of the 

 tube, the portion of it in the immediate neighbourhood of the 

 copper tube was apt to melt, and block up the tube so that the 

 gas could not continue to pass. I preferred using the triple 

 prussiate in its crystallized state, because it was easy to make 

 an allowance for the water which it contained ; whereas had I 

 dried it, 1 ran the risk of altering the nature of the very consti- 



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