50 
Selected Articles. 
portions of the two principles which constitute almost the 
whole mass of these concrete juices. 
Lemery, Baume &c. were right in thinking that the action 
of heat, however regulated, will always cause a volatilization 
of a portion of the essential oil they contain. Hence this agent 
should never be had recourse to when the crude gums can 
be used, and preference should always be given to the for- 
mula which requires the least possible quantity of excipient, 
to avoid the inconvenience resulting from a prolonged eva- 
poration ; great attention must also be paid to the regulation 
of the heat, and above all to the uninterrupted stirring or 
agitation of the ingredients, as a neglect in this particular 
will inevitably cause disappointment, as regards the expected 
results. 
In my experiments the proportions of excipients I have em- 
ployed for 250 grammes of the resin to be purified, are : 
When the fragments or tears are separate, or but slightly 
coherent, as in gum ammoniac : 
When the fragments are coherent or agglutinated, as gal- 
banum and sagapenum : 
or Water for a 1st treatment, 500 ) 
Alcohol at 22° for a 2d " 125 J 
In each operation, I endeavoured as much as possible to 
give the gum resins their original consistence. Those which 
were treated with alcohol, were dissolved as is usual, by the 
assistance of a gentle heat, and in carefully closed vessels. 
As to the treatments with acetic acid and water, they were 
limited to a solution of the substance to be purified, in one 
or other of these fluids, by the aid of moderate heat and con- 
tinued stirring, and the subsequent separation of the impuri- 
ties, by straining through a coarse cloth, and finally a con- 
centration of the product. 
Alcohol at 22°, 
or White vinegar at 3°, 
or Water, 
1000 grammes, 
500 
375 " 
Alcohol at 22°, 
or Acetic acid at 3°, 
1000 grammes, 
500 « 
