38 Historical Sketch of Improvements in [July, 



It had been hitherto believed that this change was owing to 

 the escape of half the ammonia ; but it is obvious from the 

 preceding analysis of Mr. Philhps, that an atom of carbonate of 

 ammonia (one atom carbonic acid + one atom ammonia) must 

 escape. 



The first of these salts then is a sesquicarbonate of ammonia, 

 the second a bicarbonate. (See Quarterly Journal, vii. 294.) 



4. Carbonates of Soda. — Mr. Phillips has shown that carbonic 

 acid and soda are Hkewise capable of uniting with each other in 

 three proportions ; namely, 



(1.) Carbonate composed of 1 atom carbonic acid + 1 atom 

 soda +11 atoms water. This is the common crystallized car- 

 bonate of soda of the shops. 



(2.) Sesquicarbonate composed of three atoms carbonic acid 

 -{- two atoms soda + four atoms water. This is the salt which 

 occurs native in Africa, and is known by the name of natron. It 

 is formed when a current of carbonic acid is passed through a 

 solution of common carbonate of soda in water, or when such a 

 solution is exposed to the action of an atmosphere of carbonic 

 acid by being placed in a brewer's fermenting tun. 



(3.) Bicarbonate composed of two atoms carbonic acid + one 

 atom soda, and formed by forcing carbonic acid into a solution 

 of carbonate of soda by means of a strong pressure. (See Quar- 

 terly Journal, vii. 296.) 



5. Hydrocyanate of Ammonia. — In the Annals of Philosophy, 

 XV. 394, I have given the characters of hydrocyanate of ammo- 

 nia. I do not know whether these characters had been previously 

 known to chemists ; but they were new to me, and I have never 

 met with any account of them in any chemical work. It preci- 

 pitates the greater number of metals white, and the precipitates 

 are often redissolved by agitation, or by nitric acid. I obtained 

 the salt in colourless and transparent crystals, when prussian 

 blue, or rather ferrochyazate of iron, was exposed to a red heat 

 in a copper tube. 



6. Carbonate of Potash. — M. Guibourt has shown that when 

 we wish to procure a pure carbonate of potash by burning a 

 mixture of nitre and cream of tartar, we must take a mixture of 

 two parts by weight of tartar for one part of nitre, otherwise we 

 do not decompose the whole of the saltpetre. If the mixture be 

 thrown in portions into a red-hot hessian crucible, a great deal 

 of hydrocyanic acid, or rather of cyanogen, is formed, and on 

 dissolving the residue in water, we obtain a cyanodide of potash 

 which is not easily decomposed. To obtain the carbonate of 

 potash pure, the best way is to throw the mixture into a crucible 

 scarcely heated to redness. (Jour, de Pharm. v. 58.) 



7. Mnrialfs of Potash and Soda. — When 50 grammes of 

 muriate of potash are dissolved in 200 of water contained in a 

 vessel capable of holding 320 grammes of that hquid, the ther- 

 mometer biuks during the solution 20^° ; the same quantity of 



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