ON THE STRENGTH OF SOLUTIONS OF PHOSPHORIC ACID. 191 
acid, after being melted, would refuse to congeal again until much below temperatures 
at which it had previously remained solid. 
J)r. Attfield referred to some analogous cases, especially that of a saturated solution 
of sulphate of soda. 
Dr. Parkinson said that the laws of heat in connection with change of state, from 
solid to liquid and the converse, wo.uld account for the phenomena alluded to. 
ON THE STRENGTH OF SOLUTIONS OF PHOSPHORIC ACID 
OF VARIOUS DENSITIES. 
RY MR. JOHN WATTS, 
SENIOR TELL SCHOLAR IN THE LABORATORIES OF TIIE PHARMACEUTICAL SOCIETY. 
• 
The utility of a table which shows at a glance the percentage strength of a 
solution whose specific gravity is known, will at once, I think, be admitted by 
all. The force of this is shown by the fact, that many years ago, MM. Bineau 
and Otto compiled the first table of the kind,—sulphuric acid being the sub¬ 
stance operated upon ; this was soon afterwards followed by nitric and hydro¬ 
chloric acids by Dr. Ure ; and still more recently by another for ammonia. Ine 
other alkalies, potash and soda, have also been tabulated by Dalton and Funner - 
maun ; acetic acid by Dr. Mohr; and alcohol by Fownes. These, I believe, are 
all which, up to the present time, have been so worked upon. 
Knowing the great advantage such tables present to the practical chemist, 
more particularly in saving of time and labour, I undertook, as a subject for 
the Pharmaceutical Conference, to compile a table of phosphoric acid, so as to 
exhibit at once the relation between its density and its strength. . . . Although 
a table for phosphoric acid is not so indispensable as one for sulphuric or nitric 
acids, its use in the arts and manufactures being much more limited, still phos¬ 
phoric acid is coming into much greater use, at least in medicine, and any one 
who has had the work of making the “ Syrup of Phosphates ” which are now so 
fashionable, knows the advantage accruing from the possession of a ready means 
■of obtaining a knowledge of the strength of his solution.. 
In the compilation of a table of this kind, the first thing is to know at what 
specific gravity to start; accordingly, finding that a thick syrupy acid of 1'5 
sp. gr. contained nearly 50 per cent, real P0 5 , I made that the starting-point, 
and proceeded regularly downwards as far as sp. gr. 1-006. The interval be¬ 
tween these two numbers contains 47 sp. gravities, therefore 49 in all, and as 
each sp. gr. was analysed at least three times, in order to obtain a correct mean, 
it entailed the work of about 150 analyses. The table, when completed, stands 
as follows:— 
Specific 
Gravity. 
Per¬ 
centage. 
Specific 
Gravity. 
Per¬ 
centage. 
Specific 
Gravity. 
Per¬ 
centage. 
Specific 
Gravity. 
Pex- 
centage. 
Specific 
Gravity. 
Per¬ 
centage. 
1-508 
49-60 
1-392 
40-86 
1-293 
32-71 
1-185 
22-07 
1-081 
10 - 44 * 
1-492 
48-41 
1 1-384 i 
40-12 
1-285 
31-94 
1173 
20-91 
1-073 
9"53 
1-476 
47-10 
1-376 
39-66 
1-276 
31-03 
1-162 
1973 
1"066 
8-62 
| 1-464 
45-63 
1 1-369 
39-21 
1-268 
30-13 
1-153 
18-81 
1-056 
7-39 
' 1-453 
45-38 
1-356 
38-00 
1-257 
29-16 
1-144 
17-89 
1-047 
6-17 
| 1-442 
44-13 
1-347 
37-37 
1-247 
28-24 
1-136 
16-95 
1-031 
4*15 
| 1-434 
43-95 
1-339 
36-74 
1-236 
27-30 
1-124 
15-64 
1-022 
3-03 
1-426 
43-28 
1-328 
36-15 
1-226 
26-36 
1-113 
14-33 
1-014 
1-91 
1 1-418 
42-61 
1-315 
34-82 
1-211 
24-79 
1-109 
13-25 
1-006 
*79 
1-401 
41-60 
1-302 
3349 
1-197 
! 
1 23-23 
1-095 
12-18 
_ 
* British Pharmacopoeia. 
