METHODS FOR PROXIMATE ANALYSIS. 1027 



surreptitiously. lu any case there can no possible harm result from 

 labeling. 



The same arguments may be repeated almost word for word in the 

 case of copper. 



Lead, tin, and zinc are not usually added intentionally, but are often 

 present, and can not be otherwise described than as dangerous to health. 

 Zinc is sometimes used as a substitute for copper in greening peas, but 

 t comes into canned goods accidentally as a rule. Lead comes from 

 the lavish use of solder rich in lead and from the use of low grades of 

 tin plate. As to its dangerous nature there can be no question. Tin 

 in many instances is almost unavoidably a constituent of canned goods 

 where the common unvarnished cans are used. There are few samples 

 of these goods in which it can not be detected. 



SCOPE OF THE INVESTIGATION. 



The directions given by the Chief Chemist for carrying out the work 

 on canned vegetables provided that analyses be made of the com- 

 monly occurring brands in order to establish their nutritive value and 

 that preservatives, metallic contaminations, and other foreign sub- 

 stances, be searched for. Furthermore, directions were given to exam- 

 ine a few of the tin cans to ascertain the quality of tin plate and solder 

 in common use. In accordance with these instructions crude fiber, 

 albuminoids, digestible albuminoids, ash, salt, fat, and carbohydrates 

 were determined in each sample. The preservatives looked for were 

 boric acid, salicylic acid, benzoic acid, sulphurous acid, saccharin, and 

 hydronaphthol. In working upon metallic contaminations, copper, lead, 

 tin, and zinc were searched for, and determined in many instances. 



METHODS FOB, PROXIMATE ANALYSIS. 

 GENERAL EXAMINATION. 



The full can was weighed, opened, the juice poured off, and the can 

 reweighed. The can was then completely emptied and once more 

 weighed. The difference between the first and last weighings gave 

 the total contents of the can ; that between the second and third the 

 solid contents, together with what moisture adhered thereto. 



The moist solid matter was put into a mortar, thoroughly disinte 

 grated, and mixed with the fluid. Portions of this mixture were dried 

 to constant weight at 100 in a steam -heated oven. In the bath used 

 this required about four hours. The loss gave the total water and 

 other substances volatile at the temperature mentioned. 



The rest of the pulped sample was placed on ordinary china plates 

 and dried at 100 in a steam-heated bath. When the sample became 

 dry enough to grind it was scraped off the plate, ground in a drug mill, 

 and sifted through a sieve having holes 1 mm in diameter. All glob- 

 ules of solder were picked out as far as possible before grinding. Those 



