ASSAY OF ARSENICAL DIPPING FLUIDS. 17 



The directions for executing the test read as follows : 



1. Use regular outfit. Measure 25 c. c. of bath into wide-mouth bottle and add 1 blue 

 tablet. When entirely dissolved, add 1 red tablet, and after this has entirely fallen to 

 powder gently but continuously swirl the bottle for 3 minutes, then let it stand for 7 

 minutes more with an occasional mixing. 



2. Next add test fluid from the graduate until the blue color ju^t remains perma- 

 nent for at least 10 seconds throughout the whole of the well-mixed liquid. Add but 

 a few drops at a time toward the end and avoid excess, but pay no attention to the 

 actual volume of test fluid added at this stage. 



3. Now add two white indicator tablets and agitate till mostly dissolved. Fill the 

 graduate to upper mark (zero) with test fluid, adding it just as in the estimation of 

 "actual arsenious oxid" until the blue color just reappears permanently, avoiding 

 excess. 



The number of cubic centimeters of test fluid thus added to bring back the blue 

 color represents hundredths of 1 per cent of "total arsenic" in the bath. 



If "oxidized arsenic" is present in only very small amount the 

 results are likely to be somewhat low, owing to some formation of 

 arsenious sulphid, but in any event such small amounts of "oxidized 

 arsenic" are without significance. Again it is obvious that the 

 quantity of thiosulphate used will not show the presence of ' ' oxidized 

 arsenic" in amount much over 0.2 per cent of the bath, but this 

 appears amply sufficient, for if so much is present, in addition to the 

 actual arsenious oxid, which of course is determinable in practically 

 any amount, the bath certainly should not be used for dipping. 



THE INTERPRETATION OF RESULTS. 



The "standard arsenical solution" is recommended by the bureau 

 for use in two strengths — -first, 10 pounds of white arsenic and 25 

 pounds of sal soda to each 500 gallons, and, second, 8 pounds of white 

 arsenic and 24 pounds of sal soda to each 500 gallons of bath. The 

 theoretical percentages of arsenious oxid will therefore be prac- 

 tically 24 hundredths of 1 per cent for the 10-25 formula, and 19 

 hundredths of 1 per cent for the 8-24 formula. Practical experience, 

 however, has shown that the baths work with perfect satisfaction 

 so long as the percentages of "actual arsenious oxid" do not drop 

 below the following limits: For the 10-25 formula, 22 hundredths 

 of 1 per cent; for the 8-24 formula, 175 thousandths of 1 per cent. 

 These figures therefore represent minimum percentages below which 

 the contents of the respective baths in "actual arsenious oxid" 

 should not be allowed to fall. The maximum allowed percentages 

 of "actual arsenious oxid" should be but little above the theoretical 

 figures; say, 25 hundredths of 1 per cent for the 10-25 formula and 

 20 hundredths of 1 per cent for the 8-24 formula. 



Respecting the maximum allowable percentages of "total arsenic," 

 it is not yet possible to make any statements based upon positive 

 experimental evidence. One might tentatively set the following 

 limits which experience has indicated to be within the margin of 

 safety: 30 hundredths of 1 per cent for the 10-25 formula; 25 hun- 

 dredths of 1 per cent for the 8-24 formula. 



o 



