332 C. M Munroe on the estimatimi of Phosphoric Add. 



sulphide it was found that some of the phosphoric acid was 

 always precipitated with it. Its presence was proved b}^ Bun- 

 sen's test with the magnesium wire. The salt was then dis- 

 solved in a solution of potassic cyanide and a current of sul- 

 phydric acid passed through, but with the same result as 

 before. Again it was thought that the phosphoric acid might 

 be precipitated directly from the cyanide solution by ammonio- 

 magnesic chloride, but experiment showed that the cyanide 

 contained so much cyanate and carbonate that, although the 

 solution was boiled and chlorhydric acid was added to it, accu- 

 rate results could not be obtained. 



As the ignition of the nitro-mercurous phosphate with the 

 non volatile metallic oxides, in order to drive off the mercury, 

 promised well, this process was then tried in the following manner. 



The dried salt was thoroughly mixed with a weighed quan- 

 tity of cupric oxide in a platinum crucible and the filter placed 

 on top. The whole was ignited, at first gently, then to low 

 redness, at the mouth of a muffle,* then cooled, a few drops of 

 nitric acid added to oxidize the cupric oxide reduced by the 

 filter, and then re-ignited. The ignition was continued until 

 the weight became constant. The increased weight was the 

 phosphoric oxide (P^ O J. After ignition the cupric oxide and 

 phosphate came out of the crucible in a beautiful coherent mass, 

 leaving it perfectly clean and unharmed. 



Disodic Phosphate.~lX is quite difficult to obtain this salt 

 anhydrous. It becomes so between 30° and 40°, but, as it 

 fuses at 35°, it must be repulverized for analysis, and as it is 

 quite hygroscopic, it is liable to change during the operation. 

 A quantity dried over sulphuric acid was used, the phosphoric 

 oxide being determined by ignition. 



(1) 1-1130 grras. gave -ioYG grms. Na^P^O^ = 2r98 'V^O, 



(2) 1-2355 " " -5075 " " = 21-97 " 

 le process with cupric oxide gave the 



(1) 1-0245 grms. gave -5124 grms. Y^O^ = 50-01 50-00 



(2) 1-2198 " « -4716 " " = 38-66 21-9/ 



(3) -9200 " « -2018 " " = 21-93 



(4) 1-2423 « " -2730 " " = 21-97 

 Number one was a specimen of anhydrous phosphate. 



will be noticed that the second analysis is much too high. 



* Justice is not done the muffle furnace. It gives an even, mellow heat w^^^ 

 can be easily regulated, and for igniting precipitates it is unequaled. I "^^® .-te. 

 spoken of the difficulty found in burning the filter with the alutninic P^" PJ^^^t 

 By placing it at the mouth of the muffle I was able to ignite it in the "^"^'f ^^gt 



