6 



SOLUBLE ARSENIC OXID (PROVISIONAL). 



SOLUTIONS REQUIRED. 

 The same solutions as those used in the preceding method. 



METHOD. 



To determine the soluble arsenic oxid, an aliquot portion of the water extract ! 

 from the determination of soluble arsenious oxid above (about 200 cc) is 1 

 transferred to a flask, made slightly alkaline with sodium hydroxid, and 

 evaporated to about 25 cc on a hot plate. The flask is then removed and ; 

 allowed to cool to about 80 C and an equal volume of concentrated hydro- j 

 chloric acid and 3 grams of potassium iodid added. It is allowed to stand 15 } 

 minutes, the iodin set free is exactly used up with tenth-normal thiosulphate 

 (using starch if necessary), and the solution neutralized with sodium carbonate. 

 It is again made slightly acid with hydrochloric acid, taking care that all lumps 

 of sodium carbonate are acted on, then made alkaline with an excess of sodium 

 bicarbonate, and titrated with iodin, using starch as indicator. From this 

 figure is subtracted the figure representing the amount of soluble arsenious 

 oxid, and the remainder is calculated as arsenic oxid. 





 COPPER CARBONATE. 



COPPER OXID. 

 SOLUTIONS REQUIRED. 



The same solutions as those described under the determination of total copper 

 in paris green are used. 



METHODS. 



A weighed quantity of the substance is dissolved in nitric acid and the same 

 method of analysis employed as given under the determination of total copper 

 in paris green, Method I being official and Methods II and III provisional. 



POTASSIUM CYANID. 

 CYANOGEN (OFFICIAL). 



SOLUTION REQUIRED. - 



A twentieth-normal solution of silver nitrate. 



METHOD. 



A large quantity of the sample is weighed out in a weighing bottle, dissolved 

 in water, and made up to a definite volume. Aliquot portions of this are taken 

 for analysis. The twentieth-normal silver nitrate solution is added a drop at a 

 time with constant stirring, until one drop produces a permanent turbidity. In 

 calculating the results, one equivalent of silver is equal to two equivalents of 

 cyanogen, according to the following equation: 



2 KCN + AgNO :! = KCN.AgCN + KN0 3 . 

 CYANOGEN AND CHLORIN. 



SOLUTIONS REQUIRED. 

 Same as preceding method. 



METHOD. 



The cyanogen is determined as in the preceding method. After this is done a 

 few cubic centimeters of a dilute potassium chromate solution are added and the 



