PRESERVATION OF FRUIT. 377 



products free from influences deleterious to health. To facilitate 

 sealing the jars are generally small of about one pound capacity. 

 Tin cans have many defects, but their use is very extensive, and 

 in the United States they are almost exclusively employed. In 

 California they are manufactured of a size that, when filled, they 

 weigh 2J Ibs., while in the Eastern States, as well as in England, 

 they weigh, filled, only 2 Ibs. Complaint has been frequently 

 made that the use of tin cans is deleterious to health because they 

 contain lead, which is dissolved by the vegetable acid and trans- 

 ferred to the fruit-syrup. In reply it has been said that only the 

 inferior qualities of tin contain lead, and that only in an infini- 

 tesimal quantity ; but it cannot be denied that the solder may 

 readily become injurious to health, and in cases of poisoning ex- 

 amined in the United States and in England, it could every time 

 be shown that the respective cans were soldered on the inside. 

 In England, if we are correctly informed, soldering the cans in- 

 side is now prohibited, and the passage of a similar law in the 

 United States is agitated. At any rate the time is very likely 

 not very distant when such soldering will be entirely done away 

 w T ith, if only for competitive reasons. To completely overcome 

 all complaints against solder, as well as against a content of lead 

 in the tin, cans are now manufactured in England which are pro- 

 vided inside with a thin coating whereby the contents are pro- 

 tected from contact with the metal. The insoluble constituent of" 

 this coating consists of silicate of lime or glass-powder previously 

 treated with hydrofluoric acid, while the soluble constituent is 

 silicate of soda or of potash. Any silicate of earthy bases or 

 metals may be used, or a precipitated gelatinous silicate. The 

 alkali is fixed or removed by means of a bath containing a dilute 

 solution of hydrofluosilicic acid, or a dilute solution with any other 

 suitable acid. For preparing the composition mix the soluble 

 with the insoluble silicate. The tin plates are coated with this 

 mixture by means of a brush, or dipped in a bath of it and then 

 dried by heat. The plates thus acquire a glass-like coating, 

 which remains fixed no matter IIOAV the plates may be handled 

 and worked.* 



* In this country some packers of lobsters, shrimps, etc., line the cans with 

 parchment paper. 



