73° POISONS : THEIR EFFECTS AND DETECTION. [§ 949 . 
precipitate which may form. If the latter is found to be sulphate of 
baryta, it must be derived from some soluble salt, such as the nitrate or 
the chloride. The substances which have been exhausted with water 
are now treated with hydrochloric acid, and to the acid filtrate sul¬ 
phuric acid is added. If sulphate of baryta is thrown down, the baryta 
present must have been a salt, insoluble in water, soluble in acids— 
probably the carbonate. Lastly, the organic substances may be burned 
to an ash, the ash fused with carbonate of soda, the mass, when cool, 
dissolved in HC1, and the solution precipitated with sulphuric acid. 
Any baryta now obtained was present probably in the form of sulphate ; 
nevertheless, if obtained from the tissues, it would prove that a soluble 
salt had been administered, for (so far as is known) sulphate of barium 
is not taken up by the animal fluids, and is innocuous. 
The sulphate of barium is identified as follows 
1. A part of the well-washed precipitate is boiled with distilled 
water, filtered, and to the filtrate a solution of chloride of barium added. 
If there is no precipitate, the sulphate can be none other than baric 
sulphate, for all the rest, without exception, are soluble enough to give 
a slight cloud with baric chloride. 
2. The sulphate may be changed into sulphide by ignition on char¬ 
coal, the sulphide treated with HC1, the solution evaporated to dryness, 
and the resulting chloride examined spectroscopically ; or, the sulphide 
may be mixed with chloride of calcium, taken up on a loop of platinum 
wire, heated strongly in the flame of a Bunsen burner, and the flame 
examined by the spectroscope. 
3. A solution of the chloride, of barium obtained from (2) gives 
a yellow precipitate with neutral chromate of potash, insoluble in water, 
but soluble in nitric acid. 
