No, 38.] eee ictal 
(d.) 346 grams of Rochelle salt ink 80 grams of caustic soda are 
dissolved in water and made up to one litre. 
The solutions are kept separate and mixed together in equal volumes 
when a test is made. 
2. An acid solution of ferric sulphate containing about 40 grams of 
ferric sulphate, and 40 c. c. of concentrated sulphuric acid to the litre. 
3. A solution of potassium permanganate of known strength. A | 
convenient solution is prepared by dissolving 3.5 grams of the com- 
mercial salt in one litre. 
The preparation of a standard solution of potassium permanganate, 
by dissolving a definite weight of the salt to a given volume, without 
testing its value, as has becn recommended by some chemists, is liable 
to lead to grave errors as the salt obtained in thejmarket is seldom pure. 
Solution (3) may be standardized with iron or oxalic acid in the 
usual way, but it is more satisfactory to find its value in sugar directly, 
as in this way the error due to different concentrations of the sugar 
solution may be avoided. 
The standardizing is accomplished with a two per cent solution of 
sugar as follows: Four gramsof pure cane sugar are dissolved in about 
150 c. c. of water in a 200 c. c. flask, and twoc. c. of concentrated 
hydrochloric acid added. It is then heated one-half hour on the 
steam bath to invert. After cooling, the acid is neutralized with 
sodium carbonate, and the flask filled to the mark with water. The 
solution now contains invert-sugar equivalent to two grams of cane 
sugar in 100c.c. From this solution other solutions are prepared 
containing invert-sugar equivalent to .25 gm., .5 gm., 1 gm. and 1.5 
gms. of cane sugar, respectively, in 100 ¢. c. 
Ten c. c. of one of these solutions is added to fifty c. c. of Fehling 
solution, in a flask of about 200 c. ¢. capacity. The Fehling solution 
is not heated before adding the sugar solution, as more uniform re- 
sults have been obtained when the solutions were mixed cold. The 
flask is heated over the lamp till the liquid begins to boil, when it is 
removed to the steam bath and kept hot for ten minutes. The con- 
tents of the flask are filtered, while hot, throngh an asbestos filter, 
prepared, in a funnel, as directed for the filtration in the estimation of 
crude fibre in fodder analysis. ‘The red oxide of copper that remains 
in the flask need not be removed, but is washed by decantation with hot 
water, pouring the liquid through the filter. The filtration and washing 
are facilitated by the filter pump, and is accomplished in two or three 
minutes. When washed the precipitate, with the filter, without al- 
lowing it to dry, is returned to the flask in which the reduction took 
place, and 100 c. c. of the solution of ferric sulphate added. Any 
particles of the precipitate that adhere to the funnel may be removed 
by pouring a portion of the ferric sulphate solution through it. The 
flask is then corked and vigorously shaken for a moment till the pre- 
cipitate is entirely dissolved. ‘The solution of potassium permangan- 
- ate is now run into the flask from a burette, till it imparts a slight 
color to the liquid and the quantity required noted. 
This operation should be repeated two or more times with each solu- 
tion of sugar prepared, the mean of the results obtained giving the 
amount of permanganate corresponding to a given strength of sugar 
solution. " 
