1052 FOODS AND FOOD ADULTERANTS. 



tion of statistics is necessary before the absolute innocuousnesa of oft-repeated small 

 doses can be declared. It appears a logical conclusion that the introduction of cop- 

 per in the green ing process is to be viewed with suspicion, and therefore prohibited; 

 but this conclusion would have less weight were it shown that copper existed 

 in equal quantity in any of the iisual foods of which experience has shown the 

 inuocuousness. 



The quantity of copper found by different chemists in A r arious samples of peas, 

 beans, etc., varies widely, running all the way from 20 to 222 ing of copper per 

 kilo, this being a tolerably wide range. In many instances more was found than 

 was requisite for coloring purposes. The results would probably have reached a 

 higher figure had "haricots verts," "ecossdes," or "flageolets" been added to the 

 list of those samples examined. The variations may be partly due to the different 

 absorbent powers of the different vegetables. It is also due in part to the blame- 

 worthy practice of some cauners of introducing a small quantity of copper sulphate 

 into the liquor in the can just before sealing. Pasteur found a maximum of 100 

 mg of copper per kilo of vegetables (after pouring off the juice) ; Bussy found 

 10 mg; Galippe, 60; and Carles, 210 mg. 



In the course of our own work on this subject we wished not merely to determine 

 the copper, but also to answer the serious question whether lead is introduced into 

 the animal economy by means of the tinning and solder habitually employed by the 

 canners. 



In determining the heavy metals by the method adopted the dried substance mois- 

 tened with nitric acid is carbonized in a platinum dish at a low temperature over 

 a glass lamp and in a room free from floating dust. The char is then finely ground 

 and treated with water acidulated with nitric acid. The carbon filtered off is easily 

 burnt at a low red heat. The filtrate and washings are evaporated to dryness. 

 They do not generally contain any copper. To this residue is added the ash resulting 

 from the burning of the carbon. The mixture is heated till no more nitric fumes 

 are given off, burned, water added, boiled and cooled, and filtered after twenty-four 

 hours. The lead and tin remain on the filter and the copper passes into the filtrate 

 in the form of sulphate. This is easily precipitated with a two-cell Buusen battery, 

 the filtrate being rendered moderately acid. Wash at the end of forty-eight hours by 

 successive dccantations and Aveigh as metallic copper. Lead remains as sulphate, tin 

 as metastannic acid, on the filter. Boil the residue several hours with a little crys- 

 tallized barium hydrate. The lead passes iuto the state either of hydrate or of 

 barium plumbate: tin becomes a stannate. Treat with hydrochloric acid, heat and 

 filter through glass wool. Wash with boiling water, acidulated with hydrochloric 

 acid, to extract all the lead chlorid, and mix the filtrate with boiling hydrochloric 

 acid. From this solution tin and lead are precipitated by hydrogen sulphid. The 

 sulphide are collected on a filter, washed with water charged with hydrogen sul- 

 phid, and digested in a little dilute, tepid solution of alkaline polysulphid, which 

 dissolves out the tin and leaves the lead. Precipitate the tin from the resulting 

 solution by a few drops of acid and calcine the sulphid after having oxidized it 

 with nitric acid to some extent. The residual lead sulphid from the separation is 

 transformed into sulphate by nitric acid and weighed as that salt. 



The maximum amount of tin found was 71 mg; of lead 7.7 mg per kilo. It may 

 be said of tin, as of copper, that its action on the animal economy is uncertain in 

 such small doses, but in the case of lead, even the small portions found in the vege- 

 tables examined must be regarded as a serious matter. The source of lead is gen- 

 erally the solder. In making a tin can there are left three lines of solder, one at each 

 end and another down the center of the can. Pieces of solder are also often dropped 

 in in sealing the can, and this increases the danger. This solder consists of two parts 

 lead and one part tin. A further aggravation of the dangers existing from these 

 sources is found in the employment of cheap tin plate, the cheapness of which is in 

 direct ratio to the amount of lead found in the tinning alloy. 



