79 



to stand for a few minutes, and then filter. If the resulting 

 nitrate is cloudy, gelatin is present in the milk. 



To the nitrate add a few drops of picric acid ; if gelatin 

 is present, it will be precipitated as a yellowish mass. 



Acid mercuric nitrate is made by mixing i ounce of mer- 

 cury with 2 ounces of nitric acid (HNO 3 ) and diluting 20 

 times with water. 



EXPERIMENT 76. TO DETECT BORIC ACID AND SULPHIDES 



IN MEAT 



(a) Cut a small quantity of lean meat into small pieces 

 and place it in an evaporating dish. Over this pour some 

 water to which a few drops of hydrochloric acid have been 

 added, and warm the whole slightly. Into the extract thus 

 formed dip a piece of turmeric paper, remove it, and allow 

 it to dry. If the paper shows a rose-red color on drying, 

 boric acid is present in the meat. 



(b) Put some sausage meat into a dish, and add a small 

 quantity of zinc and hydrochloric acid. If sulphides are 

 in the meat, they will react with these chemicals and will 

 form hydrogen sulphide. The hydrogen sulphide, if pres- 

 ent, can be detected in the following manner : Dip a piece 

 of filter paper, moistened with lead acetate, into the meat 

 solution. If a black precipitate forms on it, hydrogen sul- 

 phide is present and sulphides have been used in the meat 

 as preservatives. 



EXPERIMENT 77. TO DETECT COTTONSEED OIL 



Cottonseed oil is frequently substituted for olive oil and 

 other expensive oils. Cottonseed oil is wholesome food, 



