change in color is more rapid when the concentrated aqueous solution 

 is allowed to stand exposed to the air or preserved in a well stoppered 

 bottle, than when the acid is kept in the desiccator; but even under 

 the latter condition the color gradually deepens to light yellow, deep 

 yellow, light brown and finally, after several months, to dark brown 

 or black. When the acid is dried for analysis either in vacuum or in 

 an air bath the color darkens very materially in a short time, especi- 

 ally when dried at 100° or higher. When dried at a temperature of 

 60 or 70° in vacuum the color darkens somewhat, but very slightly in 

 comparison with that produced at higher temperatures. 



Patten and Hart asserted that the acid turned dark in color on 

 drying at 110° without undergoing any decomposition. As mentioned 

 by Vorbrodt the grounds for this statement are not quite clear. A 

 striking change in color, such as inosite hexaphosphoric acid suffers 

 in drying or on mere keeping either in the desiccator or under ordi- 

 nary conditions, would very likely indicate a more or less serious 

 decomposition. 



In order to determine to what extent decomposition occurs it 

 was decided to make a series of inorganic phosphoric acid determina- 

 tions by the usual molybdate method on inosite hexaphosphoric acid 

 preparations before and after drying. While absolute accuracy could 

 hardly be expected or claimed for this method, at least comparable 

 results would be obtained when the precipitations were done under 

 similar conditions. 



One portion of the acid was dried at 105° in vacuum over phos- 

 phorus pentoxide to constant weight. It was then dissolved in water, 

 neutralized with ammonia, acidified with nitric acid, ammonium ni- 

 trate added and heated to 65°, Ammonium molybdate was then added 

 and kept at above temperature for one hour. The precipitate was 

 then determined as magnesium pyrophosphate in the usual way. 



Another portion was treated in the same manner without dry- 

 ing, the amount of moisture found on drying as above being deducted 

 from the weight taken. 



The fresh acid preparation, dried in vacuum over sulfuric acid 

 as described, contained about IS per cent, of water and it gave no 

 reaction with ammonium molybdate. It was allowed to stand in the 

 laboratory at summer temperature (about 80 or 90° F.) in a loosely 

 covered dish for three or four weeks. The color had then changed 

 to light brown. On drying at 105° in vacuum over phosphorus pen- 

 toxide for about 24 hours to constant weight it lost about 22 per cent, 

 of its weight, showing that it had absorbed about 7 per cent, of water 

 during this time. The acid contained 27.31 per cent, of phosphorus. 

 The dried preparation gave the following as inorganic phosphate : 



S3 



