170 



THE CHEMISTRY OF SOME FOODS. 



[CH. VII, 



Allow to stand until the mixture has separated into two layers. 

 Remove the upper layer by the special pipette shewn in fig. 28, 



collecting it in a glass evaporating 

 basin that has been weighed. Add 

 5 cc. of ether in such a way as to 

 wash down the sides of the cylinder. 

 Remove this as before. Repeat the 

 washing with 5 cc. of ether four 

 more times. Evaporate the mixed 

 ethereal solution to dryness on a 

 water bath or a special electric 

 heater. Place the dish in a desic- 

 cator over sulphuric acid until its 

 weight is constant. 



Important Note. The greatest care 

 is necessary when evaporating off ether 

 in open basins. It is advisable to place 

 the dish on a boiling water bath, the 

 flame having just previously been turned 

 out. No other flame should be in the 

 vicinity. When the evaporation becomes 

 slow, remove the dish, reboil the water, 

 turn out the flame and then replace the 

 dish. It is safer and more convenient to 

 use an electric heater. 



Fig. 28. Pipette arranged to 

 remove the upper layer in 

 Meig's method of fat ex- 

 traction. The end of the 

 tube A is placed just above 

 C, the surface of the division 

 between the two layers . The 

 upper layer is then forced 

 out through A by blowing air 

 into the space above B. 



Lactalbumin. 



197. Boil the nitrate B, ob- 

 tained in Ex. 194. A coagulum of 

 lactalbumin is obtained. (See note 

 to Ex. 37-) 



198. Examine the filtrate A, obtained in Ex. 188. Add a drop 

 or two of litmus, and note that the reaction is distinctly acid. Boil, 

 and whilst boiling add 2 per cent, sodium carbonate, drop by drop,, 

 until the reaction is only faintly acid. A coagulum of lactalbumin 

 is formed. Filter this off and reserve the filtrate (C). 



NOTE. On boiling the acid solution, the lactalbumin is converted to- 

 metaprotein (Ex. 29). On neutralising the metaproteins are precipitated, and 

 since the solution is boiling they are coagulated (Ex. 47). The solution must 

 not be made alkaline, for this would cause the earthy phosphates to be pre- 

 cipitated. 



