the whole to a 200 cc. flask by means of a jet of hot water. This transference, with care, can be made very complete. Add sodium sulphid and digest on the water bath until all arsenious sulphid has gone into solution, leaving the copper sulphid behind; cool, make to the mark, mix thoroughly, and filter off 100 cc. through a dry filter, rejecting the first few cc. The solution thus obtained is warmed, and made acid with hydrochloric acid, which reprecipitates the arsenious sulphid and a large amount of free sulphur; filter and wash; extract the still moist precipitate on the filter with ammonia; wash the residual sulphur; reprecipitate the filtrate with hydrochloric acid, without heat; filter in a Gooch crucible; wash; dry at 100° C.; extract the remaining free sulphur with carbon disulphid; dry at 100° C., and weigh; repeat extraction and drying until constant weight is obtained. From the arsenious sulphid compute arsenious oxid. While this method leaves much to be desired, it is the best we could find to work on mixtures of this kind. The old method, as described in many text-books, of treating the mixed sulphids of copper and arsenic with sodium sulphid and filtering the entire arsenic solution thus obtained from the copper sulphid left behind did not work in the hands of the author, since in most cases the copper sulphid would commence to run through the filter directly after washing was begun.

Iron. The iron in these compounds is determined by precipitating with ammonia directly in the presence of arsenic and copper.

Calcium and magnesium.—These two substances are determined by first precipitating out the copper and arsenic with hydrogen sulphid, then precipitating the iron with ammonia, and finally determining calcium by means of ammonium oxalate in the usual way, and magnesium in the filtrate by means of sodium phosphate in the ordinary

manner.

Sulphur trioxid.-This constituent is determined as barium sulphate by precipitating sulphur trioxid from the hydrochloric acid solution of the substance in the ordinary manner.

In determining the lead and arsenic oxids in "Swift's Lead Arsenate," the compound is first dissolved in fuming nitric acid to get rid of all organic matter. It is then evaporated to drive off most of the acid and transferred to a measuring flask, where it is made to a volume, aliquot portions of which are taken for analysis. Sulphuric acid is added to one portion and the sample evaporated on the steam bath till the odor of nitric acid ceases to come off. It is now diluted with water and filtered, washing with water slightly acidified with sulphuric acid, till the precipitate is free of arsenic. This filtrate is saved. The filter and contents are washed with 60 per cent alcohol till free of sulphuric acid, dried, and finally burned and weighed as lead sulphate, using the usual precautions mentioned for this compound. To the filtrate add ammonia till slightly alkaline and magnesia mixture in the usual man

ner, and finally weigh the arsenic acid as magnesium pyro arsenate, after having ignited with the precautions mentioned in Fresenious. The results will be slightly low in both cases.

This sample has as much copper oxid as the ordinary sample of Paris Green and even more arsenious oxid, so that it is as strong or stronger in those constituents which kill insects.

It is high in both sand and sodium sulphate, faults which could easily be remedied by more careful handling and more washing.

As to the free arsenious oxid, this is above the standard used in California and the East, but below the 6 per cent standard. Since this compound has been used in practical experiments with good results by a number of the experiment stations, this is only one more point in favor of adopting the 6 per cent rather than the 4 per cent limit for free arsenious oxid in Paris greens and other compounds.

a See correspondence with manufacturers, page 59. Since Green Arsenoid is often spoken of as Scheele Green in publications by entomologists, it might be as well to call attention to the fact that these two compounds are not identical. Scheele Green is copper hydrogen arsenite and contains less arsenious oxid and more copper oxid than Paris Green, while Green Arsenoid is one of the copper arsenites not containing any hydrogen, but being richer in arsenious oxid than Paris Green and containing about the same amount of copper oxid. It is this neutral arsenite that has been recommended by the Department of Agriculture.

Although this sample contains large quantities of arsenious and copper oxids, it is worthless as an insecticide, since it contains such large quantities of soluble arsenious oxid.

This compound consists essentially of a mixture of Paris Green with about 35 to 36 per cent gypsum. The principal use of the gypsum appears to be to weaken the compound and add weight. It may also be of value in mitigating the injurious effects of the free arsenious acid. Since this compound contains even more than the 6 per cent limit of arsenious oxid, it can not be recommended as a high-grade insecticide. If the amount of soluble arsenious oxid could only be reduced to a slight extent this would doubtless be a good insecticide, since it contains enough poison to kill insects; it is at the same time in a very fine condition and will consequently stay in suspension in water better than the ordinary sample of Paris Green.

This substance consists of large amounts of gypsum, calcium carbonate, and magnesium carbonate, amounting in all to about 65 per

a See correspondence with manufacturers, page 62.

cent, along with about 13 per cent calcium arsenite, 12.53 per cent copper oxid, and small amounts of other substances. It is of value as an insecticide as far as its 13 per cent of calcium arsenite is concerned. As to the copper, this seems to be present entirely as copper oxid. A full discussion of why copper in this condition can be of little or no value as a fungicide is given in Farmers' Bulletin 146 of this Department.

This compound consists of a mixture of about 40 per cent Paris Green and 60 per cent of the ingredients used in making Bordeaux Mixture."

The 6.86 per cent of soluble arsenious oxid at once condemns this compound for all spraying purposes.

This compound is of value as an insecticide as far as its content of Paris Green, amounting to about 36 per cent, is concerned. The remainder, consisting of calcium sulphate, sand, ferric oxid. and alumina, is inert in its action on insects.

a For a discussion of the causes why Dry Bordeaux Mixture thus prepared can in all likelihood never be a success, see Farmers' Bulletin No. 146, of this Department.

The sulphur, carbolic acid, tobacco, arsenious oxid, and copper oxid, in so far as they go (about 8 per cent) are of value as either insecticides or fungicides, but the remainder is inert in its action on insects. It is possible that the gypsum present in this compound is used to act as a mitigating agent upon the active substances mentioned above.

The only substances present in this compound which have any value as insecticides are copper oxid and arsenious oxid, and these are present in very small quantities. If mixtures containing as small amounts of arsenious oxid and copper oxid as this will kill insects, it would be much better for the consumer to buy a pound of Paris Green and mix it with about 75 pounds of gypsum, thus obtaining 76 pounds of the preparation at a cost of about 50 cents, while if it was bought already prepared, it would cost retail about $3.80.

a See correspondence with manufacturers, page 61.