USE OP PRESERVATIVES. 1029 



water atul glycerol, using for every kilo of fat-free pancreas 3 liters of lime water and 

 1 liter of glycerol, p. g. 1.23. Add further a little chloroform, and set the mixture 

 aside for from four to six days. Press the mass through a bag and filter the fluid 

 through a coarse filter. Warm the fluid to 40 for two hours and refilter. The solu- 

 tion used in digestion is prepared by taking 250 cc of this extract and mixing with 

 it 750 cc of water containing in solution 5 grains of sodium carbonate. Warm to 

 40 for two hours and filter. It is then ready for use. 



From the fact that canned goods always contain heavy metals, it was 

 impracticable to determine the ash in the platinum ash dishes usually 

 employed in this laboratory. An efficient and satisfactory substitute 

 was found in the lids which are furnished with porcelain crucibles. 

 Burning was done in a gas-heated muffle, on the floor of which was laid 

 a piece 01 asbestos perforated at intervals. The rings were knocked off 

 the lids and the slight residual projection was accommodated in the 

 holes of the asbestos. Some little care is necessary in picking up the 

 dish thus formed with the tongs. It is best to put one jaw of the tongs 

 under the dish and the other above, thus picking it up sidewise, as 

 from the slanting conformation of the sides of the dish an attempt to 

 grasp it as an ordinary dish would be grasped is hazardous. These lid- 

 dishes change very little in weight from use, and from their shallow- 

 ness, permitting free access of air, a good ash is readily obtained. They 

 are best marked with hydrofluoric acid. They seldom break. 



SALT. 



The ash obtained as above described was washed into a 100 cc flask 

 with water and enough dilute nitric acid added to make the mixture 

 blue congo paper. To this solution powdered calcium carbonate was 

 added till there was a distinctly visible excess, and the solution boiled 

 long enough to expel carbonic acid. After cooling it was made up to 

 the 100 cc mark, filtered, and an aliquot part, usually 50 cc, measured 

 into a beaker and titrated with tenth-normal silver solution, using 

 potassium chromate as an indicator. Duplicates by this method are 

 concordant. 



"CORRECTED ASH." 



In the tables the result found by subtracting the per cent of salt from 

 the per cent of ash is recorded* as " corrected ash." 



PRESERVATIVES. 



The use of preservatives is becoming quite common in the canneries. 

 Some goods, corn for instance, are rather difficult to sterilize by short 

 periods of heating, and with others heat exercises an influence upon 

 the flavor or consistency, so that the addition of an antiseptic materi- 

 ally facilitates the canner's work. 



If a can of food is heated to a temperature Kiimcieut to kill all grow- 



