RESEARCH POR ARSENIC AND ANTIMONY. 539 
been used in the first instance, and the distillation has been 
slowly conducted by a regulated sand-bath heat. 
Second stage —conversion of Chloride to Hydride .—The liquid 
in the receiver is a solution of chloride of arsenic in water, 
or, as some believe, a mixture of hydrochloric and arsenious 
acids. It is in general colourless, when care has been taken; 
or if slightly coloured yellow, this will not interfere with the 
subsequent steps of the analysis. It contains no amount of 
organic matter which can lead to frothing in Marsh’s tube, 
or to any deceptive results from the combustion of the gas 
produced. There is no loss by volatility at ordinary tem¬ 
perature, since the water retains the chloride of arsenic; but 
at the same time it is proper either to proceed immediately 
with the examination of it, or to place it in a stoppered bottle 
to prevent loss by evaporation of the distillate. The arsenical 
liquid in this state may be preserved for examination at any 
future period. 
If a quantitative analysis is required in this stage from a 
given weight of the organic solid or liquid, one third of this 
distilled liquid may be reserved for the purpose. Of the 
remaining two thirds, a small portion may be diluted with 
four or five parts of distilled water and boiled. When boiling, 
a piece of bright copper foil (free from arsenic) should be 
introduced. If there is chloride of arsenic in the liquid, even 
up to the 1 -4000th of a grain, its presence will be indicated 
by a change of colour, and by the deposit of a dark metallic 
film on the copper. If the liquid should be too much diluted 
for this purpose, it may be concentrated on the polished 
copper, and the deposit will after a time be apparent. If 
the quantity of arsenic present is believed to be very small, 
the surface of copper introduced should be proportionably 
small. 
The larger portion of the distilled liquid should now be 
introduced into a bottle or flask, the capacity of which must 
be regulated by the quantity of acid liquid to be examined. 
To the neck of this flask there should be fitted, by means of 
a soft cork, a hard glass tube of about a quarter of an inch in 
the bore. After rising an inch or two, it should be bent at 
a right angle, and carried horizontally for the length of a 
foot. It should then be bent at another right angle, for the 
convenience of dipping into liquids contained in glasses or 
tubes. The horizontal portion of the tube should be drawn 
out in three different places, until the diameter of the tube 
does not exceed the tenth of an inch. This allows of the 
collection of metallic deposits in a concentrated form, and on 
surfaces in which they may be easily examined and tested. 
