ENTOMOLOGY. 473 



In 45 samples of Paris green, "neither the amount of moisture nor sand is in any 

 case sufficient to be objectionable. As to sodium sulphate, which is always present 

 in samples of Paris green on account of the method of manufacture, there is no reason 

 why a sample which had been at all well washed should have more than 1 per cent 

 present. The table shows that 16 of the samples of Paris green have between 1 and 2 

 per cent, 2 have between 2 and 3 per cent, and one has between 3 and 4 per cent, 

 making a total of 19, or 43 per cent, which have more sodium sulphate than should 

 be allowable. ... 



"The figures for total arsenious oxid show that no green contains less than 56.20 

 per cent. There are 7 greens containing between 56 and 57 per cent, 24 containing 

 between 57 and 58 per cent, 11 containing between 58 and 59 per cent, and the 

 remaining 3 containing between 59 and 62 per cent. These figures would seem to 

 indicate that there is no reason for a sample of Paris green containing less than 56 

 per cent of total arsenious oxid, and that the States having laws regarding this sub- 

 ject should change them so as to require the presence of 56 instead of 50 per cent of 

 arsenious oxid. 



"The figures for copper oxid vary from a minimum of 27.58 to a maximum of 

 31.16 per cent. More than half of the samples contain between 30 and 31 per cent. 



" If the Eastern and California standard of 4 per cent be adopted for free arsenious 

 oxid, and the 10-day water extraction method be used, there are only 13 samjiles, or 

 29 per cent, of the above Paris greens that would pass; but if the 6 per cent limit, 

 which we consider the better, be used, 38 samples, or 84 per cent, of the greens 

 would be accepted. ... 



"The figures representing the soluble arsenious oxid by the sodium-acetate- 

 extraction method seem to show that most supplies of Paris green really contain very 

 little arsenious oxid as such. . . . 



" It appears from the work that has been done on the subject that the sodium- 

 acetate method gives more closely the true percentage of free arsenious oxid in the 

 sample of Paris green, while the water-extraction method gives the percentage of free 

 arsenious oxid in the green plus some arsenious oxid obtained by the decompos- 

 ing action of the water on the Paris green. In some very coarse samples of Paris 

 green, which are supposed not to be made as well as the finer samples, the author 

 found recently that the sodium-acetate-extraction method gave very low figures 

 for free arsenious oxid (showing that only a small amount of free arsenious oxid 

 as such was present), while the water-extraction method gave very high figures 

 (seeming to show that although only a smali amount of arsenious oxid was present in 

 the free state, there was present a certain portion of the green, which was in a very 

 loose combination, and consequently was easily broken up). That portion of the 

 green which w-as in such a loose combination would, in all likelihood, when applied 

 to the plant soon break up and scorch the foliage. It therefore appears that while 

 the sodium-acetate-extraction method, as before mentioned, gives more closely the 

 actual percentage of free arsenious oxid present in the green, the water-extraction 

 method gives some idea of its stability, and consequently will express more closely 

 the value of the compound in actual orchard practice." 



It is suggested that in adding lime to Paris green to prevent the scorching of the 

 foliage, it would be better, from a theoretical standpoint, "to mix the green, in sus- 

 pension in water, with the lime about 10 days before use and stir the mixture occa- 

 sionally, since the free arsenious oxid does not go into solution in much less time than 

 this, and consequently is not acted upon as well by the lime to form the less harmful 

 compound calcium arsenite." 



In 11 samples of London purple, the water varied from 1.87 to 4.9 per cent, and 

 the sand from 1.36 to 9.74 per cent, although the latter was rarely over 3.5 per cent. 

 It was found that the arsenic was not jiresent exclusively as calcium arsenite, ))ut 

 "both as calcium arsenite and calcium arsenate. The amount of these two sub- 



