224 
PHARMACEUTICAL MEETING. 
way be separated from it; it was, in fact, still a chemical compound of boracic 
acid and cream of tartar,—a body which might be compared to emetic tartar, 
with boracic acid in the place of oxide of antimony. Having found that the 
body had not undergone decomposition, his next object was to ascertain how 
far it was still soluble or insoluble in water. In its original condition, as had 
already been stated, it was very soluble, and it was, in fact, commonly called 
“ soluble cream of tartar.” On putting some of it, previously reduced to 
powder, into cold water, it was found that it did slowly dissolve to some ex¬ 
tent. At first it appeared almost entirely insoluble, for it might be left for 
hours in water without solution to any appreciable extent, but after the lapse 
of days it did slowly dissolve, even in cold water; whilst, if it were heated to 
the boiling-point, it could be at once dissolved, and brought back to its 
original condition. It might therefore be looked upon still as chemically the 
same substance, which had undergone a remarkable molecular change, giving 
a great degree of insolubility to a body which, in its ordinary condition, was 
exceedingly soluble. 
After having thus far examined this substance, he felt a desire to make a 
similar examination of some of the other bodies before referred to. Chemical 
books generally represented the change in “pulled sugar” and in arsenious 
acid to be referable to crystallization ; but, upon examining those substances 
as he had examined this, he felt quite satisfied that this was an entire mistake 
and delusion, and that both “ pulled sugar ” and opaque arsenious acid had 
no crystalline structure whatever, but were cases analogous to the present, 
and did not justify the view generally adopted. He must add, however, that 
several more modern chemical writers had spoken more cautiously, and de¬ 
scribed the changes referred to as cases in which possibly the substances 
passed into a crystalline condition. 
It was generally represented in books that solid bodies were capable of exist¬ 
ing in two states,—the crystalline and the amorphous. The vitreous was un¬ 
doubtedly an amorphous state, and the change from the vitreous to an opaque 
state had therefore been generally looked upon as a change to the other ad¬ 
mitted condition, viz. that of a crystalline structure. He thought, however, 
it was necessary to admit that the same body in the amorphous condition 
may be either vitreous or pulverulent, that is, in the granular condition 
which he had spoken of. 
With the view of further elucidating the questions relating to borotar- 
trate of potash, he had made some experiments to determine the extent to 
which, when dissolved in water, it was susceptible of diffusion through a 
colloid septum. On a former occasion he had brought the subject of diffu¬ 
sion, and especially that department of it called dialysis, under the notice of 
the Society, and since that period he had made a great number of experiments 
to ascertain the degrees of diffusibility of different preparations used in me¬ 
dicine. According to the received notions, bodies might be divided into two 
classes, viz. the crystalloidal and the colloidal. As the result of the investi¬ 
gations of Mr. Graham, it was found that those bodies which diffused most 
readily were those which possessed a crystalline character, and that those 
which were devoid of such a character were, as a rule, bad diffusers, either 
refusing to pass through a colloid septum, or doing so only to a small extent 
and very slowly. 
How it was obviously a point of some importance practically to the physi¬ 
cian to know, among pharmaceutical preparations, what their properties are 
in these respects. Taking, for instance, the class of preparations of iron, of 
which a great number were used in medicine ; being administered by the 
mouth they passed through the intestinal canal, and the stomach and intesti¬ 
nal canal forming a dialysing apparatus, it was important to I now which of 
