140-141] DAIRY PRODUCE 5 1 



sidue becomes white. Warm the ash with a few drops of 

 strong hydrochloric acid. Evaporate the filtrate to dryness 

 and dissolve the residue in a few drops of water. Place in 

 the dish a piece of turmeric paper and evaporate to dry- 

 ness on the water-bath. A brown colour which turns 

 dark green with ammonia indicates boracic acid. 



Formaldehyde. — Place about 10 c.c. of the milk and an 

 equal volume of strong hydrochloric acid in an evaporating 

 basin. Add one drop of very dilute ferric chloride. Heat 

 slowly with constant stirring to a temperature a little below 

 boiling. A violet colour indicates the presence of formalin. 

 Care should be taken not to boil the milk or the colour may 

 be destroyed. 



Note. — This test may be used for the presence of 

 formalin in other substances than milk, but as the proteids 

 of milk take part in the reaction a few c.c. of pure milk 

 must be added to the suspected liquid before the test is 

 applied. 



Butter 



Butter consists principally of the fat of the milk, but 

 it also contains small quantities of curd, salt, and water. 



140. Water in Butter. — Place as much butter as 

 you conveniently can in a test-tube. Then hold the tube in 

 hot water until the butter is completely melted. Note the 

 appearance of the tube. The pure butter-fat will form a 

 clear top layer. Beneath this will come a cloudy layer 

 containing the curd and salt, and beneath this, again, will 

 be seen drops of water. 



141. Curd in Butter. — Whilst the butter is still hot 

 pour it on to a dry filter-paper in a funnel. Place the funnel 

 in the neck of a 4-oz. conical flask and place the whole 

 arrangement in the steam-oven (22). This will serve to 

 keep the butter melted whilst it is filtering. In a few 

 minutes nothing will be left on the paper but the curd and 



£2 



