260 
PHARMACEUTICAL KOTICES. 
when six fluid ounces of liquid have distilled, especially 
when the receiver is enveloped in the refrigerating liquid 
as it should be. It is more easy to judge by the decrease 
of liquid in the retort than by its increase in the receiver, as 
follows : After pouring into the retort the diluted sulphuric 
acid, introduce the solution of prussiate with the exception 
of six fluid ounces, and when the retort is in position for 
the distillation, mark with slips of pasted paper the level on 
either side. The reserved solution is then introduced, and 
the process proceeded with until the level of the liquid in 
the retort is marked by the pieces of paper. 
The heat should be applied with a sand bath, as direct 
heat almost invariably causes violent concussions due to the 
insoluble Everitts' salt formed, and which cause the projec- 
tion of the colored liquid into the neck of the retort and 
thus contaminate the product. A sheet iron bowl of rather 
greater diameter than the retort filled in with sand between, 
is the best arrangement when lamp or gas heat is used. 
The object of placing water in the receiver is to absorb 
the vaporous hydrocyanic acid at first liberated, which 
would otherwise, unless the refrigeration was very com- 
plete, rupture the luting or the vessel. In addition to the 
receiver, the neck of the retort should be kept cool by a 
constant stream of cold water, unless, indeed, a Liebig's con- 
denser is used, which is greatly preferable. 
The most difficult step in the process, and that involving 
the most care, is in ascertaining how much water of dilu- 
tion the distilled product requires to reduce it to exactly the 
strength of two per cent. The Pharmacopoeia merely gives 
the direction to add as much distilled water as is sufficient 
to make 100 grains accurately saturate 12 -7 grains of silver, 
a direction very difficult to follow literally, and then requir- 
ing repeated trials. It is much better to base the calcula- 
tion on the quantity of cyanide of silver produced by an 
acid of the strength sought, which is ten grains. All that 
is necessary is to weigh 100 grains of the stronger acid from 
