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and transfer the remainder to a small tared filter. Wash the residue with 50
cubic centimetres of distilled water, and dry at a temperature of 212 degrees
Fahrenheit until it ceases to lose weight, and weigh the deposit remaining.
The weight of such deposit must not exceed 40 milligrammes.
7. In order to ascertain whether the sample develops a putrefactive odour,
proceed as follows:—
Fill a bottle of about six ounces capacity with the effluent and place it
in an incubator kept at a temperature of 98 degrees Fahrenheit for a
period of three days. At the end of this period remove the bottle from
the incubator, and if the effluent has become black, and has developed an
offensive odour, it does not comply with the standard.
8. The impurity figure shall be calculated in the following manner:—
The albuminoid ammonia in grains yielded by one gallon of the effluent
shall be multiplied by 50, and the amount of oxygen absorbed from
permanganate of potash in three hours by one gallon of the effluent shall
be multiplied by 5. The sum of the two figures so obtained shall be
the impurity figure.
9. The amount of albuminoid ammonia yielded by the effluent shall be
ascertained in the following manner:—
(а) Shake the effluent vigorously and withdraw 70 cubic centimetres
by means of a pipette. Transfer this to a suitable flask in which
has been placed 430 cubic centimetres of pure distilled water, free
from ammonia. Add 1 cubic centimetre of a 10 per centum
solution of anhydrous sodium carbonate and distil over 250 cubic
centimetres to remove the free ammonia ;
(b) Now add to the liquid remaining in the flask 50 cubic centimetres
of alkaline solution of permanganate of potash containing .8 per
centum of permanganate of potash, and 20 per centum of caustic
soda or potash. Distil over 150 cubic centimetres and estimate
the amount of ammonia in the distillate. The number of milligrammes
of ammonia thus obtained from 70 cubic centimetres of
the effluent represents the number of grains of albuminoid
ammonia yielded by one gallon.
10. The oxygen absorbed shall be determined in the following manner:—
Into a flask capable of holding about 150 cubic centimetres, place 70
cubic centimetres of the well-shaken effluent. Then add 5 cubic
centimetres of a .395 per centum solution of permanganate of potash
and 10 cubic centimetres of a 25 per centum solution of pure sulphuric
acid. Place the flask, after inserting the stopper, in an incubator at a
temperature of 98 degrees Fahrenheit and allow it to remain for a period