19:2 
BRITISH PHARMACEUTICAL CONFERENCE. 
I would next notice the method employed for its analysis. After essaying 
and testing the various advantages of a great many different processes, of which I 
will speak hereafter, I came to the conclusion, that with a pure solution of phos¬ 
phoric acid, no method is more simple, more accurate, or less liable to error, than 
the method employed in the Br. Ph., viz. u the evaporation down of a weighed 
quantity of the solution, with a known excess of pure protoxide of lead.” 
I confess I was somewhat disappointed when first employing this method, 
owing to the discordant results obtained, notwithstanding that at first sight it 
seems exceedingly straightforward and plain ; but I afterwards found it entirely 
arose from not operating with pure oxide. I had used the commercial article, 
and though previous to each analysis it had been carefully ignited, there never¬ 
theless remained so much carbonate and other impurities, as to render it prac¬ 
tically worthless, no two results agreeing nearer than 2 or 3 per cent. 
Finding this to be the case, I looked about for some other substance to use 
instead, and for this purpose tried the oxide of zinc. Analysis with this latter 
oxide gave perfectly accurate results as regards numbers, but was, however, 
open to a great objection, inasmuch as the phosphate of zinc readily fuses, 
and upon ignition towards the end of the analysis to get rid of the last traces 
of water, the phosphate fusing, and adhering tenaciously to the bottom of the 
crucible, from which it cannot be subsequently removed, entirely spoils the vessel 
for a second operation. Oxide of magnesia answered no better, for this, unlike 
the oxides of lead and zinc, forms a hydrate when put into water; and, as is 
the case with many magnesia salts, either the last traces of this water of hydra¬ 
tion, or the atom of basic water assimilated when neutralizing theFO r ,isso 
difficult to totally expel, even after powerful ignition, that one can never be 
certain that the whole of the water is driven off unless the capsule has been 
allowed to cool and re-ignited several times, which, with such a number of 
similar analyses, causes much unnecessary trouble. I tried also the volumetric 
nitrate of uranium process, but as the results never approach nearer than five 
to six per cent., a discrepancy too great to be allowed in a case like this, it was 
given up. Determined then to revert again to oxide of lead, and to prej>are 
a pure oxide myself, I took red lead (2Pb()+Pb0 2 ), and dissolving out the 
protoxide with dilute nitric acid, washed well the resulting binoxide; this, by 
careful ignition over an air flame, loses its extra oxygen atom, and passes with 
incandescence to the state of protoxide. Working with oxide prepared in this 
manner I obtained highly satisfactory results, and subsequently used this me¬ 
thod only for the completion of the analysis of the table. By examining the 
gradation of the numbers on the table, we see that the percentage increases or 
decreases regularly according as the specific gravity rises or falls, proving that 
the strength can be correctly deduced from a knowledge of its density, and that, 
unlike acetic acid, it presents no anomaly in this respect; also, that when a 
strong acid is diluted with water, though a considerable quantity of heat is 
evolved, no condensation in volume follows. The correctness of the numbers 
may be also somewhat checked in the following manner :—Take 100 fluid 
grains of 1*508 acid, this will weigh 150*8 grs., and contain 74*79 grs. by weight 
°- ^^ 5 ; dilute this with 100 fl. grs. of water, the whole will weigh 250*8 grs., 
and contain 74*79 grs. by weight of F0 5 ; each 100 parts by weight will be 
therefore of sp. gr. 1*254, and contain theoretically 29*7 parts by weight of 
acid ; by referring to the latter sp. gr. on the table we find by experiment sucli 
number to contain 29TG per cent. Again, 100 fl. grs. of acid 1*285 sp. gr. will 
weigh 128*5 grs., and contain 41*03 grs. by weight of FO s ; diluted with 100 
fl. grs. of water, will weigh 228*5 grs., and contain 41*03 grs. of acid, being of 
sp. gr. 1*142; each 100 parts of this sp. gr. should contain then 17*9 by weight • 
of P0 5 . Reference to the table shows us 17*89 percent. I have checked a 
great many numbers in this manner, and they all come correct. 
