BOROTARTRATE OF POTASH. 
223 
deal of attention of chemists and pharmaceutists, for it bad been found tliat 
they differed with regard to solubility, the vitreous variety being generally 
represented as the more soluble in water of the two, but there was a great 
discrepancy in the statements of writers on this point. Here, again, the 
change had generally been represented as one in which arsenious acid passed 
from the vitreous to the crystalline condition, and opaque arsenious acid was 
usually represented as consisting of a mass of minute crystals. Then, again, 
there was another case of a somewhat similar nature,—the body known as lleau- 
mur’s porcelain or devitriffed glass,—glass which had passed from a vitreous 
condition and become opaque. When glass was exposed to long heating, espe¬ 
cially when imbedded in sulphate of lime, or something of that description, 
it lost its transparency, and became white and opaque, assuming the appear¬ 
ance of porcelain, and in that state it was called devitriffed glass, or Keaumur’s 
porcelain. There, again, the change had been ascribed to a sort of crystalli¬ 
zation, and it had been assumed rather than demonstrated, that that opaque 
glass consisted of a mass of minute crystals. Hence, no surprise need be mani¬ 
fested at the fact that in the notice on the cover of the Journal, the subject be¬ 
fore them was represented, as that of a remarkable crystallization ofborotartrate 
of potash. This borotartrate of potash, or soluble cream of tartar of pharmacy, 
had been made for many years in various ways,—by combining boracic acid 
and cream of tartar, or borax and cream of tartar. The boracic acid had been 
used in different proportions, but in the Trench Codex the proportions laid 
down were 1 part of boracic acid to 4 of cream of tartar, and these proportions 
were usually employed. Neither of these substances was very soluble, the 
cream of tartar being least so ; but, by heating them together, a perfectly 
clear solution was formed, which might be evaporated down to dryness with¬ 
out any separation of solid matter taking place. Consequently the boro¬ 
tartrate of potash formed one of a class of what had always been looked upon 
as perfectly amorphous uncrystallizable bodies, which might be obtained by 
the process of scaling, like citrates of iron and other preparations of that 
description, and it was always represented in books as a perfectly uncrystal¬ 
lizable substance. It was true, however, that in a recent French work on 
pharmacy, it was stated that a molecular change had sometimes been ob¬ 
served to take place in borotartrate of potash, which became solidified and 
opaque in this manner. However, before that notice was met with, and 
when it came under his (Dr. H.’s) observation, he made a number of experi¬ 
ments on the subject. First, he had examined it under the microscope, and, 
in doing so, he failed entirely to detect anything like crystalline structure in 
this altered mass. It appeared to him, in fact, that although obviously a 
molecular change had occurred and the body had become comparatively in¬ 
soluble, from having been previously excessively soluble, there was no evi¬ 
dence of that change at all consisting in its having assumed a crystalline con¬ 
dition. The microscope indicated that there were still, throughout the mass, 
some fragments of a vitreous body. Splinters could be detected here and 
there with a conchoidal fracture, indicating clearly the vitreous condition of 
those portions. Some few of these fragments still remained, but the great 
mass consisted of minute globular particles. In fact it was curious to ob¬ 
serve some of these splintered vitreous portions, covered as it were with a 
species of pollen, so that they had the appearance of having been dusted over 
with a white opaque powder. So much for the microscope. He had been 
induced to think that possibly a change of the nature of what chemists called 
dissociation had taken place, and that the cream of tartar and boracic acid 
had separated from each other; if that were so, of course the boracic acid 
might be easily obtained by solution in alcohol. A portion therefore was 
powdered and boiled with rectified spirit, but no boracic acid could in that 
