ON COMMERCIAL PHOSPHORIC ACID. 
265 
The method ordered in the B. P., i.e. noting the increase of weight in some 
oxide of lead, after digestion with the acid, will of course be open to the 
same objection as the uranium process, because the phosphate of ammonia 
will be decomposed by the oxide of lead and the whole of the acid thus ac¬ 
counted for. I have not made any use of the B. P. process, as it occupies 
RESULTS OF EXAMINATION OF SAMPLES OF DILUTE PHOSPHORIC ACID. 
No. 
Per cent, 
of P0 5 . 
Specific 
gravity. 
Remarks. 
B.P. . . . 
10-0 
1-080 
B. L. . . 
8-7 
1-064 
1 . . . 
10.4 
1-074 
1 
• 
2 . . . 
10-0 
1-064 
> Up to B. P. 
3 . . . 
100 
1-073 
4 . . . 
5 . . . 
93 
8-9 
1-065 
1073 
Above P. L. 
6 . . . 
8-8 
1-062 
7 . . . 
8-8 
1-061 
- About P. L. 
8 . . . 
8-6 
1-062 
9 . . . 
8-4 
1-049 
10 . . . 
8-3 
1-055 
Contains ammonia. 
11 . . . 
83 
1-057 
12 . r . 
80 
1051 
13 . . . 
SO 
1-051 
14 . . . 
8-0 
P047 
15 . . . 
7-7 
1*046 
16 . . . 
7-4 
1*055 
. Contains ammonia. 
17 . . . 
7-4 
1051 
P 
18 . . . 
7-0 
1*056 
Pm Contains ammonia. 
19 . . . 
7-0 
1-044 
r u 
d) 
20 . . . 
6-9 
1-043 
21 . . . 
6-9 
1046 
p 
22 . . . 
6-9 
1*043 
23 . . . 
6-8 
1-052 
21 . . . 
5-9 
1*041 
Contains ammonia. 
25 . . . 
5-9 
1-037 
26 . . . 
5-8 
1*035 
Contains ammonia. 
27 . . . 
5-8 
1*036 
• 
28 . . . 
56 
1-061 
Contains ammonia and 
sulphuric acid. 
too much time, and is not, I believe, practically more accurate than that with 
uranium. The most satisfactory way seemed to be to supersaturate with 
lime of known value to a certain volume, allow the precipitated phosphate of 
lime to subside, and estimate the excess of free lime in part of the clear liquid. 
This however takes considerable time. I may mention that while experiment¬ 
ing this part of the subject in various ways, and working with the colouring- 
matter of violets as an indicator and caustic potash as the neutralizing agent, 
I was struck with the fact, which seemed tolerably constant, that the red 
of the violets (in the acid liquid) was changed to blue when one-third of the 
amount of alkali had been added that was necessary to produce the green, 
which showed that the alkali was in excess. This did not always occur with 
chemical exactitude, but taken together with the tribasic character of the 
phosphates it seemed interesting and to merit further examination. Litmus 
did not show this at all, but turned a bluish-purple about when the violets 
