64 



METHODS OF ANALYSIS 



[Chap. 



3 DETERMINATION. 



Weigh an amount of the sample equal to the arsenious oxid equivalent of 250 

 cc. of the standard iodin solution, and wash into the distillation flask by means of 

 100 cc. of concentrated hydrochloric acid (sp. gr. 1.19). Add 5 grams of cuprous 

 chlorid (Cu2Cl2) and distil. 



When the volume in the distillation flask is reduced to about 40 cc, add 50 cc. 

 of concentrated hydrochloric acid by means of the dropping funnel and continue 

 the distillation until 200 cc. of the acid distillate have passed over. Then wash 

 down the condenser and all the connecting tubes carefully, transfer these washings 

 and the contents of the 3 Erlenmeyer flasks to a liter graduated flask and dilute 

 to the mark. Mix thoroughly, pipette 400 cc. into an Erlenmeyer flask and nearly 

 neutralize with a saturated solution of sodium or potassium hydroxid, using a few 

 drops of phenolphthalein as an indicator, keeping the solution well cooled. 



Continue as directed under 3 (C) beginning with "neutralize with sodium bicar- 

 bonate." The number of cc. of iodin used in this titration represents directly 

 the total per cent of arsenic in the sample expressed as arsenious oxid (AsjOa). 



FIG. 5. APPARATUS FOR DISTILLATION OF ARSENIC CHLORID. 



TOTAL ARSENIOUS OXID. 



(The following methods determine arsenic, and antimony if present, as the -ous 

 oxids, AS2O3 and Sb203, respectively. Ferrous and cuprous salts vitiate the results.) 



Method I. 

 C. C. Hedges Method,^ Modified.^— Tentative. 



6 REAGENTS. 



The reagents and solutions used are described under 3. 



7 DETERMINATION. 



Weigh an amount of the sample equal to the arsenious oxid equivalent of 100 cc. 

 of the standard iodin solution, wash into an Erlenmeyer flask with 10-15 cc. of dilute 

 hydrochloric acid (1 to 1), followed by about 100 cc. of water, and heat on the steam- 

 bath to complete solution, at a temperature not exceeding 60°C. Cool, neutralize 



