PHARMACEUTICAL MEETING. 
459 
was in every respect desirable. The amount of carbonate, whether wet or dry, 
that could be dissolved under pressure was, within certain limits, simple 
enough. They could dissolve a large quantity of magnesia under a great 
amount of pressure, but the question of keeping depended on a variety of con¬ 
ditions—upon something more than the mere fact of the volume of carbonic 
acid present in the solution. Mr. Umney had alluded to the fact that the pro¬ 
cess was rather long and tedious, and that the same result could be obtained in 
a shorter space of time. There was no doubt this was so, but at the same time 
there was something in the keeping properties due to the time during which the 
carbonate of magnesia was kept in contact with the carbonic acid gas under 
pressure. He was not prepared to say whether a different compound was ac¬ 
tually formed, but there was something more than plain carbonate of magnesia. 
Carbonate of magnesia which had been agitated for a long time with an excess 
of gas did really deposit less than a solution which was made quickly. If you 
forced carbonic acid gas into the solution under a pressure of 901b. or 100 lb. 
to the square inch, you could readily dissolve a large quantity of the carbonate ; 
but it was another question altogether whether you did not get a product very 
much better by agitating the same quantity of solid carbonate, the same amount 
of fluid, and the same amount of gas, at a pressure of 30 lb. or 401b. to the 
square inch for a longer time. He was not able to speak with certainty as to 
which was really the best process ; perhaps a modification of the process would 
be, in some respects, the best. At certain pressures you could get a solution 
which kept in cold weather very well; but in summer, and in that state of the 
atmosphere w'hich was commonly called thundery, a remarkable effect was 
always produced upon this solution. If they had a solution of any given 
strength, say five grains to the ounce, they might take hundreds of bottles, well 
and carefully corked, all supersaturated with gas, and leave them for twelve 
hours during the night, and in the morning they would find perhaps 90 per 
cent, of them had crystallized and deposited. There was nothing at all to ac¬ 
count for this change, for it would happen when the temperature, though it 
might be warm, was not at all excessive, and yet down w'ould come the car¬ 
bonate. From his experience he really could not point out any process by 
which you could prepare fluid magnesia containing even ten grains to the ounce 
which would keep during all weathers ; and he had serious doubts whether it 
really could be done. Some persons had thought that this effect was due to 
the action of light, but he had found that even bottles kept in the dark had 
really deposited the most. He alluded to this to show that this w r as a prepara¬ 
tion which required very constant watching and careful preparation to get it 
into anything like a proper condition ; and when they did send it out in that 
condition, they could not always undertake to say that at the end of a month it 
should not change in any respect. As regards the variation in strength, his 
own experiments, which had been carried on for some years, had corroborated 
the result which Mr. Umney and Ur. Attfield had communicated. Some speci¬ 
mens were very weak indeed, but he apprehended that some of those examined 
w'ere really made on a large scale as by-products, and could not have been 
made specially with a view to use in medicine. The members were probably 
aware that there was one well-known process for making carbonate of magne¬ 
sia—the process, in fact, by which most of that used in commerce was made ; 
and in that process fluid magnesia was made as a by-product, contaminated, of 
course, with iron and a few other things which would occur in the magnesian 
limestone used in the process. He was charitable enough to suppose that the 
unfortunate No. 3 in Dr. Attfield’s table must have been a specimen from a 
manufacturer of that sort, and, in doing so, he did not attribute any blame to 
the manufacturer, for he did not produce the fluid magnesia as a special product 
for sale as medicine, or as containing so many grains to the ounce, flhe fact 
2 h 2 
