September 2,1871.] THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
191 
next proceeded to determine if the increase of volume 
had any relation to the specific gravity of the different 
substances, or if, when a known weight of salt was dis¬ 
solved in water, the increase of volume was in proportion 
to the volume, as indicated by the specific gravity, and 
if so, the salt would dissolve withoiit either expansion or 
contraction.” Did he really expect an ounce of sulphate 
of magnesia, for instance, to occupy the same space as an 
ounce of water! 
This method involved the use of a volumenometer. 
The one employed was not so well adapted for the attain¬ 
ment of accurate results as that of some other experi¬ 
menters, hut was, on the whole, far superior to that of 
Dalton. 
Nitrate of potash was the first salt employed in testing 
the value of his new idea. The specific gravity of nitrate 
of potash being, according to his determinations, 2 ‘071, 
one hundred grains of the salt would occupy the space 
of 48-21 grains of pure water. The calculated specific 
gravity would therefore he found thus,—100 grs. of salt 
being- dissolved in 500 grs. distilled water—• 
100 + 500 600 
48-21 + 500 548-21 “ 1 
But the specific gravity ascertained by experiment was 
1-1100, showing, according to him, a condensation 
amounting to 6-22 grain measures. 
I certainly cannot deduce this amount from the data 
given, but make it 7*7 gr. m. However, the principle 
being established, it becomes possible when the ratio of 
condensation of a salt is known, to calculate the specific 
gravity of a solution within certain limits of accuracy— 
those limits being defined by temperature and degree of 
dilution. 
The effect of dilution as exemplified in the case of a 
saturated solution of nitrate of soda is shown to be the 
following:—- 
If to 430 gr. m. of a saturated solution 60 gr. m. of 
water be added, the mass will suffer a decrease of 
volume of 1 gr. m. Sulphate of magnesia behaves in 
the same manner, and to the same degree. Nitrate of 
potash suffers a diminution of "5 gr. m., muriate of am¬ 
monia -25 gr. m. under the same circumstances. 
From a long and laborious paper by Messrs. Playfair 
and Joule, describing a series of experiments undertaken 
in order to ascertain whether there really existed any 
similarity between solid and gaseous combinations, in 
respect of the law of equal or multiple proportions ob¬ 
served first by Gay-Lussac in the case of gases,—I pro¬ 
pose to ’select those facts only that seem to have some 
pharmaceutical interest, and are possibly capable of prac¬ 
tical application, omitting reference to the theoretical 
deductions therefrom further than to say that they have 
since been roughly handled by Professor Marignac, of 
Geneva, whose criticisms appear to me to well deserve 
consideration. 
The volumenometer employed differed from that used 
by Holker, in that it had a tubulure in its side for in¬ 
troduction of salt, fitted with a ground-glass stopper. 
This admitted of the stem being of smaller diameter, and 
enabled the experiments to be attended with greater 
accuracy. 
Unfortunately, however, the experimenters, whilst 
acknowledging the disturbing effects of temperature and 
dilution, seem to have adopted no systematic method of 
procedure as to the one or the other, unless it be true 
that the particular temperatures and dilutions adopted 
were selected because the results so obtained accorded 
best with certain theories sought to be established. This 
Professor Marignac evidently points at, though he does 
not actually affirm it. 
I may mention the case of sugar as being especially 
interesting to the pharmaceutist. The volume occupied 
by an equivalent of this substance = 172 grs., varies 
according to dilution between 99-00 and 108-06 grm., 
as follows:— 
Eatio of 
Sugar and Water. 
Temp. 
Vol. in gr. m. of 
172 gr. Sugar. 
1 
20 
60 
99-00 
1 
10 
52 
105-09 
1 
1 
52 
107*01 
3 
1 
52 
108-06 
The temperatures here even are not uniform. I may 
observe that when the ratio is 1:1, the sugar occupies- 
a volume very nearly co-incident with that duo to its 
specific gravity 1-606. 
The investigation included the determination of a 
vast number of specific gravities and solution volumes of 
salts of every description. In compiling- the following 
table I have selected a few only of special interest, 
considered pharmaceutically. The specific gravities are, 
in general, not those of Playfair and Joule, but those 
obtained by H. Buignet through the use of the Air 
Volumenometer invented by Regnault; and therefore, 
I consider, more worthy of acceptance. The term “ spe¬ 
cific gravity in solution,” I employ simply to designate- 
the weight of the solvcnd in air divided by the space it 
occupies in the solvent:— 
Name of Salt. 
Sp. Gr. in 
Air. 
Sp. Gr. in 
Watery 
Solution. 
Sulphate of Copper. 
2-302 
2-77 
^ Soclci • • • • • 
1-471 
1-76 
Biborate „. 
1-692 
2-085 
Chloride of Calcium .... 
1-68 
1-98 
Potash Alum. 
1*757 
2-135 
Ammonia. 
1-653 
2-00 
Carbonate of Soda. 
1-463 
1-58 
Sulphate of Magnesia .... 
1-675 
1-96 
,, Iron. 
1-902 
2-22 
Nitrate of Potash. 
2-126 
2-80 
,, Soda. 
2-265 
3-22 
Chloride of Potassium .... 
1-986 
2-80 
,, Ammonium . . . 
1-55 
1-50 
Bromide of Potassium .... 
2-65 
4-10 
Iodide ,, .... 
2-97 
3-77 
Chloride of Sodium. 
2-145 
3-21 
„ Barium. 
3-081 
4-42 
Chromate of Potash .... 
2-68 
5-60 
Bichromate ,,. 
2-624 
3-35 
Carbonate „. 
2-10 
7*54 
Bicarbonate .. 
2-18 
3-00 
,, Soda. 
2-165 
4-70 
Oxalate of Ammonia .... 
1-47 
2-00 
Sugar . 
1-606 
1-608 
Bearing in mind the irregularity that seems to attend 
all bodies, and mixtures of bodies, on the verge of change- 
of state, and, therefore, confining oneself to solutions of 
mean condition, neither extremely strong nor excessively 
weak, it is possible by means of this table to ascertain 
beforehand, with tolerable accuracy, the effect of mixing- 
definite quantities of a salt and water, and vice versd of 
determining the proportions of both salt and water ne¬ 
cessary to produce a given specific gravity. Tims taking 
the case of sugar,—what will be the specific gravity of a 
solution containing- equal parts of sugar and water r 
The volume of the water will, of course, be 1, the volume 
of the sugar y-^, the total volume being 1-6218. Divid¬ 
ing the total weight = 2 by this, we get the specific- 
gravity = 1*23. According to the table in AVatts ‘Dic¬ 
tionary,’ the specific gravity of a solution containing 50 
per cent, of sugar is 1*2166 at the temperature 63-5 - 
Proceeding in "the same way with chloride of sodium, 
we get for a solution containing 20 per cent, ot salt 
the theoretical number 1-159, the experimental number 
being 1-1511. 
Sulphate of magnesia gives for a 30 per cent, scluticnr 
