128 EXPElilMENT STATION. [Jan. 



Pumice stone; the stone is prepared by dropping it at white 

 heat into distilled water and leaving it until required. 



Method. — Into an Erlenmeyer flask of 300 cubic centime- 

 ters capacity are brought 5 grams of fat, carefully avoiding get- 

 ting any fat on the sides of the flask; 20 cubic centimeters of 

 glycerol-soda are added and heated over a naked flame, rotating 

 continuously, until the saponification is complete, as shown by 

 the mixture becoming perfectly clear. The soap when cold 

 should be white and free from globules of fat. Many small 

 pieces of pumice stone, 135 cubic centimeters of recently boiled 

 distilled water and 5 cubic centimeters of sulfuric acid solution 

 are added, and the flask connected with a Liebig condenser^ and 

 heated carefully on gauze until a transparent oily layer of in- 

 soluble fatty acids forms on the surface; 110 cubic centimeters 

 are then distilled over in as near thirty minutes as possible and 

 received in a sugar flask. The distillate is passed through a diy 

 dense filter, to remove all traces of the higher fatty acids which 

 may have passed over with the volatile acids and appear in the 

 distillate as oily drops or white solid particles. After mixing 

 thoroughly, 100 cubic centimeters are pipetted into a small flask 

 and titrated with N/lO alkali, using 5 drops- of phenolphthal- 

 ein as indicator, avoiding entirely the addition of water. The 

 pink coloration should hold at least five minutes. Extreme care 

 should be exercised in preventing the absorption of carbonic 

 acid at all times during the process. Blank tests should be con- 

 ducted with every new lot of reagents. The titration reading, 

 minus the blank, increased by a tenth and calculated to exactly 

 a 5-gram basis, represents the Reichert-Meissl number. 



Limit of error, .25 Reichert-Meissl number. 



Synopsis of Reaction. 



C3H,(R02)3 + 3 NaOH = 3 R02Na + C3H5(OH)3 



fat alkali salt glycerol 



The added glycerol acts as a transmitter of heat and has a 

 boiling point of 290° C. 



2 RO.Na + H2SO4 = 2 RO.H + NasSO^. 



Titration of the volatile acids. 



• A vertical condensor with <i rapid circulation of cold water is advisable. 



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



