8 MASS. EXPERIMENT STATION BULLETIN 201. 



The basic products are more stable than the acid or neutral salts, due 

 evidently to the higher content of lime. 



The status of the dry commercial products is still rather indefinite. 

 Carbonate of lime is present in some instances as an impurity or filler, 

 having neither toxic nor protective action. 



Form of Gtiaranty. — Calcium arsenate is usually sold under the follow- 

 ing form of guaranty: — 



Per Cent. 



Active ingredients: — 



Tricalcium arsenate, not less than . . . . . . 76 . 00 



Total arsenic pentoxide, not less than . . . . 42 . 50 



Total arsenic (as metallic), not less than . . . 28.00 



Inert ingredients, not more than . . . . . . . . 24 . 00 



100.00 

 Water Soluble. 

 Soluble arsenic pentoxide, not more than . . . . . . 1 . 50 



Soluble arsenic (as metallic), not more than . . . . . . 1.00 



The remarks relative to the form of guaranty of lead arsenate hold 

 equally well for the form of guaranty of calcium arsenate. Note particu- 

 larly that the killing power of calcium arsenate is apparently greater than 

 that of lead arsenate on account of the higher percentage of arsenic pen- 

 toxide. Therefore a smaller quantity is used in the spray, so as to give 

 the same amount of metallic arsenic as when arsenate of lead is u.sed. 



To summarize: Both acid and neutral calcium arsenates are of rela- 

 tively high arsenic content, but too soluble to warrant their use without 

 excess lime. The basic product is of a lower arsenic content but more 

 stable. They are effective poisons, the fineness of particles and light 

 flocculent character insuring a fair power of suspension and uniform dis- 

 tribution. The white mixture indicates the leaf surface covered, and dries 

 to a film that is persistent under average weather conditions; and is, in 

 brief, an efficient and reasonably satisfactory arsenical for the more resist- 

 ant plants. 



Standard Formulas for Application. 



As previously mentioned, there is a great difference in the rapidity of 

 killing power between arsenates and arsenites. For this reason the two 

 classes of materials cannot be compared on the basis of arsenic contained. 

 The following table represents basic quantities of the several materials of 

 standard or near standard composition which may be used. Naturally 

 the amounts to be used must be varied to adapt the spray to different kinds 

 of insects, and to make it safe when used on different kinds of plants. 



