Prof. Liversidge — Chalk in New Britain. 
531 
The specific gravity was taken from a mass weighing about 
78grammes, which was allowed to soak in water for about one hour 
and a half, in fact until all air-bubbles ceased to be evolved ; a small 
quantity of the block scaled off when immersed in the water — a 
correction for which had to be made. 
The above figures show that in round numbers about 81 per cent. 
of the speeimen consists of calcium carbonate ; thus it is undoubtedly 
a far less pure limestone than the ordinary white chalk, as the follow- 
ing figures indicate. 
Chemical Composition of Chalk. 
A speeimen of chalk, from near Gravesend, which was analysed by 
Mr. W. J. Ward, yielded the following results : 
Calcium carbonate 
98-52 
Magnesium carbonate 
-29 
Calcium sulphate 
-14 
Manganese binoxide 
-04 
Phosphoric acid 
traces 
Organic matter 
— 
Insoluble matter, chiefly silica 
-65 
99-64 
Mr. David Forbes, F.R.S., also examined some specimens of chalk, 
the analyses of which are here cited ; the first analysis shows the com- 
position of a piece of white chalk from -Shoreham, in Sussex ; and the 
second of a piece of grey chalk from Folkestone. 
White chalk. Grey chalk. 
Calcium carbonate 98-40 ... 94-09 
Magnesium carbonate -08 ... -31 
Phosphoric acid I , „ 
Alumina and loss ) ’ 42 - trace 
Sodium Chloride — ... 1-29 
Water — ... -70 
Insoluble rock debris 1-10 ... 3-61 
100-00 100 00 
(Vide “ Geology of England and Wales,” by H. B. Woodward, p. 239.) 
Another sample of chalk obtained from a well at Driffield was found 
by Mr. T. Hodgson to have the following composition : — 
Moisture 5 20 
Calcium carbonate 93-30 
Magnesium carbonate -15 
Iron sesquioxide and alumina -20 
Silica 1-15 
100-00 
It is, however, far less impure than the “chalk mud ” of the 
Atlantic, for the analysis quoted by Professor Sir Charles Wyville 
Thomson, F.R.S., in his “Depths of the Sea,” p. 469, shows that the 
“chalk mud” contains merely some 60 per cent. of calcium carbonate, 
and with as much as from 20 to 30 per cent. of silica, and varying 
proportions of alumina, magnesia, iron, and other substances. The same 
author mentions that the typical chalk is free from silica, and so it 
would appear to be from the above-quoted analyses ; but the “ insoluble 
