288 
MAGNESIA AS AN ANTIDOTE TO ARSENIC. 
occasionally for a period of 8 or 12 hours ; that this pro- 
portion is removed entirely in less than 3 minutes if the 
mixture of magnesia and water be previously near the tem- 
perature of 212°; and that the same proportion is removed 
with as much speed at ordinary temperatures, if the mag- 
nesia be used in the form of gelatinous pulp, as thrown 
down in a cold solution of sulphate of magnesia by solu- 
tion of caustic potash and washed with cold water. 
It is well known that magnesia was proposed many 
years ago by Mr. Hume of London as an antidote for ar- 
senic, and that several cases have been published in which 
it appeared to have been of service ; but that its general 
utility has been doubted or denied on account of the appa- 
rent want of chemical action between oxide of arsenic and 
magnesia. M. Bussy's inquiries will probably clear up 
these difficulties. Meanwhile it appears probable, from 
the experiments described above, that the general belief in 
the want of action between magnesia and oxide of arsenic 
has arisen from the circumstance that for a long time no 
other magnesia has been in current use in medical practice 
in Britain except the dense variety, which appears to exert 
very little action on arsenic in solution on account of its 
great density. 
Dr. Christison promises more accurate experiments and 
a statement of the successful case hereafter. Meanwhile 
it appears advisable that, when magnesia is used as an an- 
tidote, and cannot be promptly obtained in the gelatinous 
state, the light calcined magnesia should alone be employ- 
ed, and in the proportion of between 30 and 50 parts to 1 
of arsenic. — Chem. Gaz. from Monthly Journal of Med 
Science. 
