REPORT OF TEE CHEMIST 181 



SESSIONAL PAPER No. 16 



In order to arrive at. the insecticidal values of these brands it will be necessary 

 to take into consideration, first, the percentage of water present. Other things being 

 equal, the paste containing the least water will be the strongest. Secondly, the 

 percentage of arsenic oxide is of importance as determining the toxic value of the 

 paste. Thirdly, the amount of impurities — soluble and insoluble — not only as 

 affecting the strength of the paste but possibly also its effect on foliage, must be 

 taken into account. In every well-made paste, that is, one in which practically all 

 the arsenic and lead are present as insoluble arsenate of lead, the efficiency or strength 

 of any brand may be approximately arrived at by subtracting the sum of the water 

 and impurities from 100 — the larger the remainder the stronger the paste. 



To determine the economic values of any number of brands it will be necessary 

 for the purchaser to calculate the cost per lb. of the arsenate of lead present in the 

 paste. An illustration may serve to make this clear. Two brands A and B, are 

 offered; the price of A, laid down, is 15 cents per lb., and it contains, approximately, 

 35 per cent of water and impurities; B is 12 cents per lb., laid down, and contains, 

 approximately, 50 per cent water and impurities. In the case of A, 65 lbs. arsenate 

 of lead cost $15, or 23 cents per lb., while in B, 50 lbs. arsenate of lead cost $12, or 

 24 cents per lb. 



With respect to sample No. 7008, the manufacturers state in the circular 

 advertising this product: 'Our prices are based on 40 per cent moisture, if the 

 analysis shows a slightly higher percentage we accordingly adjust the weight of the 

 package to figure on 40 per cent moisture content.' 



Samples Nos. 5981 and 5655 were received in a partially dried-out condition, so 

 that the analytical data do not indicate accurately the composition of the brands as 

 placed on the market. 



No. 6764 is a powdered arsenate of lead, to be used in the dust form only. It is 

 not suitable for application with water as a spray and therefore is not directly com- 

 parable with the other brands analysed, which are all pastes. 



HOME-MADE ARSENATE OF LEAD. 



In view of the difficulty which the majority of farmers and fruit growers will 

 meet in obtaining,, generally, chemicals of a known composition — and this refers 

 especially to sodium arsenate — it is not at all probable that the home preparation of 

 arsenate of lead will become popular. However, as so many correspondents have 

 written us during the past year on the matter, and so many formulae have appeared 

 in agricultural publications, we thought it desirable to examine the necessary chemicals 

 upon the Canadian market with a view to establishing the correct proportions to be 

 used in the preparation of a safe spray. The chemicals employed are acetate of lead 

 (sugar of lead) and arsenate of soda, and it is desired to mix them in such proportions 

 that there is no excess of arsenate of soda in the resultant spray, for this chemical 

 has a scojching effect upon foliage. A slight excess of acetate of lead is necessary, 

 *in order to ensure the complete precipitation of the arsenic. 



ACETATE OF LEAD. 



This chemical is of fairly uniform composition, as will be evident from the 

 following data which were obtained from samples analysed in the Farm Laboratories 

 during the past year: — 



