COLOl'R TESTS. SSI- 



is by no means conclusive of the presence of added cottonseed 

 oil, as the milk of cows fed on large proportions of cotton cake 

 yields butter whicli will give a brown coloration. 



Halphen's Test for Cottonseed Oil. — One to 3 c.c. of fat 

 are mixed with equal volumes of amyl alcohol, and carbon 

 disulphide containing 1 per cent, of sulphur, and heated in a 

 boiling brine bath for ten to fifteen minutes. A red or orange 

 colour shows the presence of cottonseed oil. If no reaction is 

 obtained a little more carbon disulphide should be added and 

 the heating repeated. 



Wellmann's Test for Vegetable Oils. — The reagent con- 

 sists of a solution of sodium phospho-molybdate. It may be 

 prepared by saturating 5 grammes of molybdic acid with sodium 

 carbonate solution, adding 1 gramme of sodium phosphate, 

 evaporating to dryness and fusing. The mass is dissolved in 

 boiling water, and concentrated nitric acid ("; to 7 c.c.) is added 

 till the yellow shade is permanent. The solution is then made 

 up to 100 c.c. 



One gramme of fat is dissolved in 5 c.c of chloroform and 

 shaken with 2 c.c. of the reagent for one minute. A ureen coldr- 

 ation (changing to blue on addition of amnicmia) is formed lu 

 the aqueous layer when vegetable oils are present. Coco-nut 

 oil is not, however, detected bv this means. 



Behaviour of Butter Fat with Solvents. 



Critical Temperature of Solution. — Crismer recommends 

 that sevoval drops of the melted and filtered fat be introduced 

 into a small tube 10 millimetres in diameter and litO to TiO milli- 

 metres long b}- means of a capillary pipette. An equal volume 

 of alcohol is added and the tube sealed and fastened by a platinum 

 wire to the bulb of a thermometer ; it is then heated in a bath 

 of sulphuric acid till the meniscus separating the two layers 

 becomes a horizontal plane. At this point the thermometer . 

 is withdrawn from the bath, and turned sharply two or three 

 times until the liquid becomes homogeneous, after which it is 

 replaced and the temperature allowecl to fall slowly, the ther- 

 mometer and tube being constantly shaken. The temperature 

 at which a marked turloidity is produced in the liquid is the 

 critical temperature of dissolution. If absolute alcohol be- 

 employed an open tube may be used. 



The alcohol used should liave a specific gravity of O'TiKiT at 

 l.jo" f. ; if the specific gravity differs 0"106" should be added 

 or deducted for each O'OOOl below or above 07967. 



When examining butter fat it is necessary to estimate also 



