§ 61. niosPHOKic ACID. 83 



bring the contents of the flas'c to a gentle boiling, and 

 continue the application of the heat until the bulb on / 

 becomes hot ; draw about 1800 c.c. of air through the 

 apparatus, by means of an aspirator connected with I, 

 then immediately separate a from /, and weigh ^ and hh' 

 again when they have become cold. The increase in 

 weight gives the carbonic anhydride. 



The tube ^ can be used several times if it is carefully 

 closed when not in use. If the tube hh^ is used a second 

 time, it will be safer to connect another with it on the 

 outside, filled in the same Avay ; if this second tube does 

 not gain in weight, the first one may be used a third time, 

 with the same precaution ; if it does gain notably, use it 

 alone in the third analysis, and re-fill AA'. 



c. It often happens that carbonic acid and chlorine are 

 to be estimated in the same substance ; in this case, after 

 making the determination of the acid by either of the 

 above methods, using, of course, pure nitric acid to set it 

 free, filter the contents of the flask if not perfectly clear, 

 and precipitate the chlorine in the filtrate and washings 

 with argentic nitrate. 



PHOSPHORIC ACID. H3PO4. 98. 



61. All phosphates except those of the alkaline metals 

 are insoluble in water, but all are soluble in acids. 



Reactions. — When a solution of a phosphate is added 

 to one of magnesia containing an ammoniacal salt and 

 an excess of ammonia, a white flocculent precipitate, 

 MgNH^PO^, is produced, which, after standing for a 

 time in a warm place, becomes more granular and crys- 

 talline ; in very dilute solutions the precipitate does not 

 appear until after long standing, and is then crystalline, 

 and adheres to the sides of the tube in the same manner 

 as described under magnesium. 



