titration with twentieth-normal silver nitrate continued to the appearance of the 

 red-brown color of silver chromate. The first titration with silver nitrate repre- 

 sents the cyanogen present according to the equation above. The second t it rat i< >n , 

 using potassium chromate as indicator, represents the cyanogen according to the 



following 



KCN.AgCN + AgN() :t = KNO 3 + 2 AgCN, 



plus the chlorin present ; therefore the second minus the first ivading represents 

 the ehlorin present in terms of silver nitrate. 



BOAP. 

 BBAL STATEMENT, 



In mo.-t -oap> u-ed by the entomologist (not considering the resin soaps) it is 

 necessary to know three constituents in older to judge of the value of the soap 

 I'or -praying purpo-es, vi/, moisture, total fatty matter, and total soda or pot a.- h. 

 The moisture an. I alkali an- usually determined and the total fatty matter a p- 

 proximately estimated hy difference. 



Moi.-i i i;i. l'i;u\ I.-IONAL). 



The following method is given hy Benedikt and I.ewkowitsch for determining 

 water in -"ap. Tare accurately a heaker of HIM cc capacity, the bottom of which 

 .\ered with recently ignite(l, perfectly dry sand about one-half inch deep, 

 together \\ith a small glass rod. 



Weigh off in a beaker about "> 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. Kvaporate 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 men- 

 tioned in the above method, vix : If the soap is hard the ."> grams should be cut 

 off in very thin strips so that it will dissolve more readily in the alcohol ; also no 

 sample- i.i -nap examined by the writer have ever come to a constant weight on 

 drying, but finally begin either to gain or to lo>e a little indefinitely. It is, there- 

 fore, he.-t to heat the soup at HOC until it is nearly dry and weigh, then return 

 the soap to the oven and dry another half hour, ('ontimie this alternate drying 

 and weighing until the weight changes only a few milligrams during the course 

 of a half hour'.-. dr\ ing. 



TOTAL ALKALI l'i;>\ I-IOXAL). 



A \\ei_rhed (plant ity of the soap is decomposed by hydrochloric acid and the 

 water is filtered off I'M i m the fat, which is \\ashed. Hot h potassium and sodium 

 in the filtrate are first determined as mixed chlorids in the ordinary manner and 

 the potassium is then determined by means of platinum chlorid. 



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

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

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

 again. Add a -mall amount of ammonium carbonate to the disk, cover and 

 heat. Repeat this a number of times till all bisulphates have changed to sul- 

 phate-. Te-i the re-idue qualitatively to determine whether it is sodium or 

 pota--Jim -ulphate, and calculate the residue to soda or potash as the case 

 may be. 



If the determination of other constituents of the soap be desired the methods 

 given on page H2 of Bulletin 68, Bureau of Chemistry, U. 8. Department of 

 ilture. have been found fairly satisfactory. 



