59^ POISONS : THEIR EFFECTS AND DETECTION. [§ 770 . 
well-stirred mass is dried and ultimately thoroughly charred and heated 
in a muffle until practically all the carbon is burnt off. When cold, 
the ash is moistened with water and 20 c.c. of dilute sulphuric acid added. 
The dish is warmed and the contents transferred to a flask of about 
120 c.c. capacity. Half a grain of potassium metasulphite is added, 
and the solution boiled until free from the smell of sulphurous acid. 
The liquid is cooled and made up to a bulk of 50 c.c. in a calibrated 
flask or measuring tube. 
The method recommended by A. Gautier and P. Clausmann ( Compt . 
Rend., 1917) is to heat the tissues arid organs in an oven at 300° until 
they become dry and friable ; they are then ground up and intimately 
mixed with two to three times their weight of pure calcium oxide, which 
is then slaked with a little water. The mass is heated in a muffle to a 
dull redness. In about two hours the ash, carbon-free, is powdered, 
extracted with water, and acidified with sulphuric acid. The mixture is 
boiled, filtered, and evaporated until white fumes appear. 
Fusion with Sodium Peroxide.— Henry F. P. Little, Ed. Cahen, 
and Gilbert T. Morgan ( Journ . Chem. Soc., T., 1909) estimate arsenic in 
organic compounds as follows :— 
0-2 to 0-3 grm. of the finely powdered substance is mixed in a nickel 
crucible with 10 to 15 grms. of sodium peroxide and sodium carbonate 
in equal proportions, and gently fused for five minutes at a dull-red heat. 
The contents of the crucible are extracted with water and rinsed into a 
450-c.c. conical flask. From 25 to 31 c.c. of sulphuric acid (1 : 1) are 
added cautiously, and the solution concentrated by boiling to 100 c.c. ; 
then 1 grm. of potassium iodide is added, and the liquid concentrated to 
40 c.c. The last traces of iodine are destroyed by a few drops of dilute 
sulphurous acid, and the bright green solution diluted considerably 
and saturated with hydrogen sulphide. The arsenious sulphide is filtered 
off, washed three times with hot water, then dissolved off the filter with 
20 c.c. of N/2 sodium hydroxide, and the filtrate returned to the 
conical flask, where it is treated with 30 c.c. of hydrogen peroxide (20 
vols.), the excess of the latter reagent being destroyed by heating. After 
the subsiding of frothing, a few drops of phenolphthalein solution are 
added, and then 11 c.c. of sulphuric acid (1 : 1), this quantity giving 
10 c.c. in excess. One gramme of potassium iodide is now added to the 
liquid, which should have a volume of 100 c.c., and is next concentrated 
to 40 c.c., when the yellow colour of the free iodine is removed by a few 
drops of dilute sulphurous acid. Cold water is added, and the diluted 
solution neutralised with 2N sodium hydroxide and just acidified with 
sulphuric acid. A certain amount of 11 per cent, sodic phosphate is 
now added, and the arsenite solution titrated in the usual way with 
standard iodine and starch. The volume of 11 per cent, phosphate added 
should be equal to the number of c.c. of iodine required in the titration. 
