CHEESE 



73 



addition of sand, is distilled with water and barium carbonate, 

 and the distillate received in a measured quantity of standard 

 sulfuric acid, and, after boihng, the excess of acid is neutral- 

 ized with standard sodium hydroxid, using rosolic acid as 

 indicator. 



Amido-compounds. — These are estimated by macerating the 

 powdered cheese in water for 15 hours at the ordinary tem- 

 perature. After adding a little dilute sulfuric acid (i : 4), the 

 proteids and peptones are precipitated by phosphotungstic 

 acid. The precipitate is filtered off and washed with water 

 containing a little sulfuric acid. The filtrate is made up to a 

 definite bulk, and the nitrogen is determined in an aliquot por- 

 tion of the liquid by the Kjeldahl-Gunning process, allow- 

 ance being made for the nitrogen existing as ammonium. 



Peptones and Albumoses. — These are determined jointly by 

 boiling the powdered cheese (mixed with sand as before) with 

 water and filtering from the undissolved casein and albumin. 

 In an aliquot portion of the filtrate the peptones and albu- 

 moses are precipitated by adding dilute sulfuric acid and 

 phosphotungstic acid. After washing with acidulated water 

 the nitrogen in the precipitate is determined by the Kjeldahl- 

 Gunning process. 



The total nitrogen of the cheese is also determined, and after 

 allowing for the nitrogen existing as other forms, the balance 

 is calculated to casein. 



Poisonous Metals. — Lead chromate has been found in the 

 rind of cheese, and finely divided lead in a number of Cana- 

 dian cheeses. In England zinc sulfate has been employed 

 under the name of cheese spice to prevent the heading and crack- 

 ing. Arsenic has also been found; it may be detected by 

 Reinsch's test. Lead, zinc, and chromium may be detected 

 by ashing a portion of the sample in a porcelain crucible and 

 applying the usual tests. 



