1412 Method of. ‘preserving the colour of the Purple Cabbage. 
In estimating these constituents according to the elec- 
tro-chemical theory, I believe that the oxide of titanium, 
notwithstanding its important agency in the analytical ex- 
periments, must be regarded as an accidental ingredient, 
as well as the oxide of iron, which in some measure may 
have been derived fromthe iron mortar. As the cymo- 
phane of Brazil appears to be constituted more conforma- 
bly to the hypothesis of chemical proportions than that of 
Haddam, the following calculation may be made, founded 
on its composition, which gives for the essential constitu- 
ents of Chrysobery], 
(Per 100 parts) 
Silica 6°61 containing Oxygen Voeaee 
. Alumina 75.79 oe Bbe38e 
~ Glucina 17.64 Fishes 6.49 
and very nearly corresponds with the following’ mineralo- 
gical formula, A*S+2GA‘%. | 
ART. VII.—Method of preservine the color of the purple 
cabbage. Extract of a letter to the Editor, from George 
T. Bowen. 
You are aware that the infusion of the common red 
cabbage is one of the best tests which we possess of the 
presence of acids and alkalies. In the variety of the 
colors which are produced in it by the addition of these 
substances, the cabbage liquor is superior to litmus, for 
it is not only like litmus reddened by acids, but is also 
unlike that substance turned green by the alkalies. The 
great objection to the cabbage !iquor asa test is its lia- 
bility to spoil, and I have never seen in the chemical 
books any method proposed of preserving it foruse. The 
red liquor which is produced by the addition of an acid to 
the infusion, may be kept for a long time uninjured ; in 
order to use it, however, it is necessary to restore its blue 
color by means of an alkali; and the delicacy of the test 
is in this manner impaired. I find that this test may be 
