614 ANNUAL REPORT OF THE Off. Doc. 



Biibstance merely to make up bulk and weight; and any samples ex- 

 hibiting such residue may be put down as fraudulently and wilfully 

 adulterated. Unfortunately, this test does not show the presence of 

 uncombined arsenious oxid, which is also soluble in ammonia, and 

 which, although it has not been considered strictly an adulterant on 

 the ground of its poisoning qualities, nevertheless its presence in 

 large quantity is dangerous to the foliage and ought to be known. 



^. Microscope Test,—T\\\'& test, unfortunately, within reach of only 

 those in possession of a fairly good compound microscope, is one of 

 the surest and quickest means of determining the grade of a sample 

 of Paris green. The value of this test as a quick means of determin 

 ing the fitness of samples for further examination, and as an adjunct 

 lo chemical analysis, was early insisted upon by the California Sta- 

 tion, and wherever this test can be performed it will prove of great 

 value and assistance, if only as a preliminary survey to a chemical 

 analysis. 



Pure Paris green under a one-quarter or one-sixth inch objective is 

 seen to consist of clean, green spheres, wholly separate and distinct 

 from one another; and in a pure sample these are all that can be 

 seen. Plate VI is a reproduced photo-micrograph of a high-grade 

 sample. A low-grade sample will have something of the appearance 

 shown in Plate VII. The clean, green spheres are in this case mixed 

 with particles of a crystalline structure, varying in shape and size. 

 The appearance of such a sample indicates the addition of free ar- 

 seniousoxid put in to fill or make up a green low in combined arsenic. 

 The pure green can in this case be as distinctly seen among the par- 

 ticles of white arsenic under the microscope ae ''wheat can be dis- 

 tinguished from dirt that might be mixed with it."* Wheo the white 

 arsenic has been put in during the process of manufacture (as is some- 

 times done) or results from careless manipulation during manufac- 

 ture, it is much more difficult to detect it. In that case the white 

 arsenic crystals are often seen sticking to the green balls themselves, 

 giving them, on the whole, a rather irregular outline and causing 

 them to cling together into masses instead of remaining separate and 

 distinct from one another.* For this reason, therefore, a chemical 

 analysis must be resorted to in order to determine these points with 

 certainty. 



But there can be no mistake about the appearance of a wilfully 

 adulterated sample. Plate VIII shows the appearance of such a 

 sample under the microscope. In this case a great number of long, 

 needle-shaped crystals are seen. They are the characteristic crystals 

 of gypsum (calcium sulphate) and there can be no legitimate excuse 

 whatever for their presence. These, together with the preponder- 

 ance of the other irregular crystals and the almost total absence of 



'Bulletin 12<. California Expeiiment Station, p. 14. 



