LONDON PURPLES. 19 



sodium-acetate-extraction figures are only 0.8S per cent, 1.17 per cent, 

 1.08 per cent, and 1.37 per cent, while the .sodium-acetate-extraction 

 figures for samples 19712, 19718, 19726, and 20368 are 8.91 per cent, 

 1.76 per cent, 3.13 per cent, and 6.37 per cent, showing that the first 

 four samples did not contain originally any more free arsenious oxid 

 than an average sample, while the second four samples did contain 

 more arsenious oxid than the average, with possibly one exception. 

 Although this course of reasoning may not apply to all Paris greens, 

 it is at least suggestive, and consequently is worthy of note. 



The figures representing the soluble arsenious oxid by the sodium- 

 acetate-extraction method seem to show that most samples of Paris 

 Green really contain very little arsenious oxid as such, and that in the 

 great majority of cases where an amount of free arsenious oxid mani- 

 festly above the average is shown by this method these samples are 

 either above or approaching to the safety limit of 6 per cent, as shown 

 by the water-extraction method. Examples of this are samples 19613, 

 19712, 19718, 19719, 19723, 19725, 19726, 20360, 20365, and 20368, 

 while exceptions are samples 19668 and 20366. 



LONDON PURPLES. 



In analyzing samples of London Purple the following determina- 

 tions were made: Moisture, sand, total arsenious oxid, total arsenic 

 oxid, calcium oxid, soluble arsenious oxid, soluble arsenic oxid, and 

 soluble calcium oxid. The methods follow." The dye is determined 

 by difference. 



METHODS OF ANALYSIS AND DISCUSSION. 



Moisture. Dry 1 to 2 grams at 100 C. for from 12 to 14 hours. 

 Report loss us moisture. 



Sand. Use sample from moisture determination. Dissolve in 

 hydrochloric acid; filter, wash, dry, and burn, calculating residue as 

 sand. 



Total arsenious oxid. Two grams of London Purple are dissolved 

 in about 80 cc of water and 20 cc of hydrochloric acid at a tempera- 

 ture of from 60 to 70 C. (not higher for fear of driving off arsenious 

 chlorid), filtered and washed to a volume of 300 cc. One hundred 

 cc of this is treated in a 500 cc flask, with sodium bicarbonate in excess. 

 The contents of the flask is then brought to the mark \vith water, 

 using a few drops of ether to destroy bubbles, and 250 cc filtered off. 

 To this is added starch solution, and the standard iodin solution, 6 until 

 the blue color appears. The result is the arsenious oxid, as such, in 50 

 cc of the original solution, that is, in 0.3333 gram. 



See article by Hay wood, Jour, of the Amer. Chem. Soc., Vol. XXII, No. 12. 

 &The standard iodm used is prepared in the same manner as that used in the 

 analysis of Paris Green. 



