ii8 
Mr. Davy on some 
has a bit of sponge inserted in a small aperture at the bottom 
of it. When a light is wanted, it is only necessary to shake 
the bottle so as to moisten the sponge with the alcohol, take 
out the stopper, and put the smallest particle of the powder on 
the moistened sponge ; it instantly becomes red hot, and will 
readily kindle one of the matches. This mode of igniting a 
metal seems to be quite a new fact in the history of chemistry ; 
but the means of keeping it in a state of ignition, is only 
another illustration of the facts previously pointed out by 
Sir H. Davy, in his late valuable researches, which have 
thrown so much light on the philosophy of flarne, and led to 
such very interesting, important, and unexpected results. 
5. On the effects of sulphate of platinum upon gelatine. 
When an aqueous solution of sulphate of platinum is added 
to any solution of gelatine, such as isinglass, size, or glue, a 
precipitate occurs, and all the sulphate is separated in union 
with the gelatine ; or if a minute portion remain, it is preci- 
pitated on boiling the fluid. This precipitate, whilst in a 
moist state, is of a brown colour, and has some degree of 
tenacity ; but when well washed and dried at a temperature 
a little above the boiling point of water, its colour changes 
to a jet black ; it becomes hard and brittle, and has a resinous 
lustre. It is not decomposed by being boiled in water or in 
weak alkaline solutions. When it is gently heated by a 
spirit lamp on a slip of platinum, a violent action is produced, 
and a dense white vapour is exhaled, in which the odour of 
sulphureous acid is perceptible, the substance becomes ig- 
nited, and is presently decomposed, leaving the reduced pla- 
tinum in small grains. 
