110 MASS. EXPERIMENT STATION BULLETIN 166. 



fectly clear. Care should be taken not to overheat and discolor the mate- 

 rial. The soap when cold should be absolutely free from globules of fat. 

 Ten grams of glass beads/ 135 cubic centimeters of recently ^boiled 

 distilled water, and 5 cubic centimeters of suKuric acid (1 to 4) are added, 

 and the flask connected with a Liebig condenser.^ (See Fig. 3.) The 

 mixture is heated on 16-mesh Ni-chrome wire gauze at low ebullition, 

 until the separated fatty acids and underlying liquid become clear. One 

 hundred and ten cubic centimeters are then distilled as nearly as possible 

 in thirty minutes, and received in a graduated flask. The flame should 



Fig. 3. — Distillation apparatus employed in the determination of Reichert-Meissl number. 



be well oxidized to induce vigorous agitation of the beads, thus assuring a 

 more thorough separation of the volatile acids. The distillate is thoroughly 

 mixed and passed through a dry, dense filter to remove all traces of higher 

 fatty acids that appear as oily drops or white solid particles. One hundred 

 cubic centimeters are pipetted into an Erlenmeyer flask and titrated 

 with N/10 alkali, using 1 cubic centimeter ^ of phenolphthalein as indi- 

 cator, avoiding entirely the addition of water. The pink coloration should 

 hold several minutes. Care should be exercised at all times during the 

 process to prevent the absorption of carbonic acid. Blank determinations 

 should be run with every new lot of reagents. The titration reading, 



' Weighing approximately one-half gram each. 



' A vertical condenser with a rapid circulation of cold water is preferable. 



» A definite quantity is necessary if the mean molecular weight is to be determined. 



