NOTE ON CRYSTALLIZED CARBONATE OF MAGNESIUM. 
511 
sophical Society of Glasgow,—Transactions of the Botanical Society of Edinburgh,— 
Journal of the Linnean Society,—Journal of the Chemical Society,—Journal of the 
Society of Arts,—Journal of the Photographic Society : from the respective Societies,— 
Specimens of “Quill ” and “Tablet ” Barks from a new Species of Cinchona, discovered 
by and imported by Sefior Pedro Kada, from Eastern Bolivia: presented by W. H. 
Peat, Esq.,—An Antique Pestle and Mortar, bearing the following inscription in 
raised capitals, SOLI DEO GLORIA, 1633 : presented by Mr. Garle,—Six Specimens 
of American pressed Herbs: presented by Messrs. B. 0. and G. C. Wilson, Botanical 
Druggists, Boston, U.S.,— Fresh Fruits of Citrullus Colocynthis : presented by Mr. 
Morson,—Specimens of Linseed and Cotton Cake, also specimens of Palm Oil and Cake: 
presented by the Curator,—Specimens of the Leaves and Bark of Cascarilla Carua , of 
Weddell: presented by Mr. Howard. 
The following papers were read :— 
NOTE ON CRYSTALLIZED CARBONATE OF MAGNESIUM. 
BY PROFESSOR ATTFIELD. 
Ordinary Magnesia alba ( Magnesias, Carbonas , B. P.) is not a simple carbo¬ 
nate, but, as is well known, a compound which may be represented as contain¬ 
ing three molecules of true carbonate of magnesium, one of hydrate, and four of 
water of crystallization (3MgC0 3 , Mg2H0,4H 2 0). When this substance is 
suspended in water, and a current of carbonic acid gas transmitted, a solution 
known as “Fluid Magnesia” results ( Liquor Magnesise Carbonatis , B. P.). On 
heating this solution, pure terhydrous carbonate of magnesium (Mg C 0 3 ,3 H 9 0) 
is precipitated, and the same compound is deposited in well-marked acicular 
crystals by the spontaneous evaporation of the liquid. If, however, the solution 
be exposed to extreme cold for any length of time, transparent crystals of a dif¬ 
ferent character are deposited ; they have hitherto been described as tabular, 
and are composed of one molecule of true carbonate of magnesium with five in¬ 
stead of three molecules of water of crystallization (Fritzsche). On exposure 
to air and light they become opaque and lose two-fifths of their water, having 
then the chemical composition of the acicular crystals obtained by evaporation, 
but totally differing in appearance. Small crystals of this tabular variety of 
carbonate of magnesium were optically examined in 1823 by H. J. Brooke, Esq., 
F.R.S. (‘Annals of Philosophy,’ vol. vi. p. 375). He found their primary form 
to be an oblique rhombic prism, which might be cleaved in two directions 
(parallel to the planes M aud M in the following figure). 
This pentahydrous carbonate of magnesium is now noticed simply to draw 
attention to some unusually large crystals of the salt recently forwarded to me 
by Mr. Barnard S. Proctor, Pharmaceutical Chemist, Newcastle-on-Tyne. The 
largest is figured in the accompanying outline; it was 13 millimetres (about \ 
an inch) long, 9 wide (about -fths of an inch), and 6-5 thick (about ^ inch). 
All had become opaque, and on analysis proved to have been converted by ex¬ 
posure into the terhydrous salt. *3240 of a gramme, analysed by my pupil 
Mr. Alfred Franklin, yielded *0945 of magnesia (MgO). One hundred parts 
gave 
By experiment By calculation 
29-167 28-988 
Of the following figures, the first is a copy of that originally drawn by Brooke, 
to show the normal form of the crystal on an enlarged scale; the second repre¬ 
sents the actual size of the largest of the crystals now noticed. By goniometric 
measurement I was able to make out every angle mentioned by Brooke, though 
at first sight, through unequal extension of some of the planes, my crystals 
differed materially from that he figured. 
