34 INSECTICIDES AND FUNGICIDES. 



potassium and sodium, washing the filter and contents, and precipi- 

 tating the calcium out of the filtrate in the ordinary way with ammonia 

 and ammonium oxalate. 







Total neutral fat and unsaponifiable matter. To determine these 

 two substances, about 10 grams of the soap is weighed out and dissolved 

 in alcohol. Fifty to 70 grams of acid washed, ignited sand is now 

 added and the alcohol evaporated off. The mass is dried and trans- 

 ferred to a Soxhlet extractor, where it is extracted with ether. This 

 extract contains neutral fat, unsaponifiable matter, and free fatty 

 acids, which are weighed together. The free fatty acids are deter- 

 mined by means of standard alkali and phenol phthalein and subtracted 

 from the other two. 



Resin acids. A rather large quantit} 7 of the soap is first dissolved 

 in water and, after heating to boiling, enough dilute hydrochloric acid 

 is added to set the fatty and resin acids free. The boiling is continued 

 till the fat collects in oily drops. The vessel is cooled and the acid 

 water poured off. The residue is again boiled with water, which is 

 again poured off. The fatty matter now remaining is washed with 

 cold water and transferred on a watch glass to a desiccator, where it 

 is thoroughly dried. The resin acids are determined in a weighed 

 quantity of this mixture by the Twitchell method. For this dissolve 

 2 or 3 grams of the mixture of acids prepared as above and place in a 

 flask in about 10 times their volume of absolute alcohol. Pass a cur- 

 rent of dry hydrochloric acid gas through the flask, which is immersed 

 in ice water. Pass the hydrochloric acid through for about three- 

 quarters of an hour, or until it is noticed that the gas is passing 

 through the liquid unabsorbed. Set the loosely covered flask aside for 

 one hour, dilute with 5 volumes of water, and boil until the water 

 layer becomes clear. Transfer to a separate ry funnel, washing out 

 all the ethylic ethers and resin acids with ether. Shake well and run 

 off the acid layer. Wash the etherial solution a number of times with 

 pure water until all hydrochloric acid is removed. Now add 50 cc of 

 alcohol and titrate the solution with standard potassium hydroxid, 

 using phenol phthalein as indicator. The resin acids combine with the 

 alkali and the ethylic ethers are practically not touched. To obtain 

 the amount of resin, multiply the number of cc of normal alkali used 

 by 0.346. One hundred parts of resin acids are equal to 97.32 parts 

 of resin anhydrid. 



