As the result of numerous tests, it has been found that genuine butter, when examined by the above method, requires from 13 to 15 c.c. of the decinormal solution. The following are the number of c.c. required by various other fats:-- Lard 0·2 Rape oil 0·25 Kidney fat 0·25 Olive oil 0·3 Sesamé oil 0·35 Oleomargarine 0·7 to 1·3 Cocoa-nut oil 3·70 Dr. Elwyn Waller[33] modifies the foregoing method of procedure by adding 50 c.c. of water to the contents of the flask remaining after the first distillation, and again distilling off 50 c.c., the process being repeated until the final distillate neutralises only 0·1 c.c. of the decinormal alkali. With butter fat, it was found that the first distillate contained about 79 per cent. of the total volatile acids present. By means of this modification, a distinction between the rate of distillation of the volatile fatty acids of different fats is possible. The non-volatile acids left in the flask are washed several times with water, in order to remove the glycerine and potassium sulphate present, and are then dried and weighed. For estimating the percentage of pure butter fat in a sample of mixed fat, Reichert employed the formula: B = 7·3 (_m_ - 0·3), in which _m_ is the number of c.c. of soda solution used in the titration. Baron Hübl[34] has recently suggested a method for butter testing, which is founded upon the fact that the three series of fats (acetic, acrylic, and tetrolic), unite in different proportions with the halogens (iodine, bromine, and chlorine), to form addition products. Iodine has been found especially well adapted to the examination of fats. The standard solution employed is prepared by dissolving 25 grammes of iodine in 500 c.c. of 95 per cent. alcohol, and adding to the solution a solution of 30 grammes of mercuric chloride in 500 c.c. of alcohol. The reagent is then standardised by means of a solution of 24 grammes of sodium hyposulphite in 1 litre of water. The test is applied as follows:--1 gramme of the sample under examination is introduced into a flask and dissolved in 10 c.c. of pure chloroform. The iodine reagent is then gradually added from a burette, the mixture being well shaken, until the coloration produced indicates that an excess is present, even after standing for about two hours; 15 c.c. of a 10 per cent. potassium iodide solution and 150 c.c. of water are then added and the excess of iodine present determined by means of the sodium hyposulphite solution, and deducted from the total quantity used. The amount of iodine (in grammes) absorbed is calculated to 100 grammes of the fat; this is termed the iodine number. The examination of numerous samples of genuine butter and oleomargarine, and other fats, made at the laboratory of the New York State Dairy Commissioner, furnished the following results:[35]--