INSECTICIDES AND FUNGICIDES. 



31 



ture, total fatty matter, and total soda or potash. The moisture and alkali 

 are usually determined and the total fatty matter approximately estimated by 

 difference. 



(b) MOISTURE a (MODIFIED METHOD OF BENEDIKT AND LEWKOWITSCH). 



PROVISIONAL. 



Tare accurately a 100 cc beaker, the bottom of which is covered about one- 

 half inch deep with recently ignited, perfectly dry sand, and in which is a small 

 glass rod. Weigh in the beaker about 5 grams of the sample; add 25 cc of 

 alcohol or more If necessary, and dissolve the soap in the alcohol by constant 

 stirring on the water bath. Evaporate the alcohol and finally dry in an oven 

 at 110 C. until the weight is constant. A few precautions should be taken 

 which are not mentioned in the above method, namely: If the soap is hard the 

 5 grams should be cut off in very thin strips so that it will dissolve more readily 

 in the alcohol ; also most samples of soap never come to a constant weight on 

 drying, but gain or lose indefinitely. It is, therefore, best to heat the soap at 

 110 C. until it is nearly dry and weigh, then return the soap to the oven and 

 dry another half hour. Continue this alternate drying and weighing until the 

 weight changes only a few milligrams during the course of a half hour's drying. 



(c) TOTAL ALKALI.& PROVISIONAL' 



Dissolve a weighed quantity of the soap in water; decompose with hydro- 

 chloric acid, filter off the water from the fat, and wash with cold water. 

 Determine both potassium and sodium in the filtrate first as mixed chlorids in 

 the ordinary manner and then determine the potassium by means of platinum 

 chlorid. 



A rapid but only approximate determination of the alkali in soap Is made in 

 the following manner : Weigh a small quantity of the soap, treat with concen- 

 trated sulphuric acid, burn, repeat treatment with sulphuric acid, and burn 

 again. Add a small amount of ammonium carbonate to the dish, cover, and heat. 

 Repeat this a number of times till all bisulphates have changed to sulphates. 

 Test the residue qualitatively to determine whether it is sodium or potassium 

 sulphate, and calculate the residue to soda or potash, as the case may be. 



7. Soda Lye. 

 (a) CARBONATE AND HYDROXID.C METHOD I (PRECIPITATION). PROVISIONAL. 



(1) SOLUTIONS REQUIRED. 



A half-normal solution of hydrochloric acid ; methyl orange and phenol- 

 phthalein indicators. 



(2) DETERMINATION. 



Weigh a large quantity of the sample in a weighing bottle, dissolve in carbon- 

 dioxid-free water, and make up to a definite volume. Analyze aliquots of this 

 solution. Titrate one portion with half-normal acid, using methyl orange as 

 indicator, and note the total alkalinity thus found. Transfer another aliquot 

 of the same size to a measuring flask and add enough barium chlorid to pre- 

 cipitate all carbonate, avoiding any unnecessary excess. Make the volume up 

 to the mark with carbon-dioxid-free water, stopper, shake, and set aside to allow 



a Benedikt and Lewkowitsch, Oils, Fats, and Waxes, p. 632. 



"Benedikt and Lewkowitsch, Oils, Fats, and Waxes, page 630; U. S. Dept. Agr., 

 Bureau of Chemistry, Circular No. 10, Revised, page 7. 

 e Sutton's Volumetric Analysis, 9th ed., page 56. 



