TOTAL PROTEIDS 73 



metallic state. Cool in an atmosphere of hydrogen and weigh. 

 The weight of copper is calculated to lactose from Table 

 LXXI in the appendix. 



The weight of lactose X 20 gives the percentage per 100 

 c.cms. of sample. As an alternative method of weighing the 

 reduced oxide, a Gooch crucible may be used in which a layer 

 of asbestos about one-quarter of an inch in thickness has been 

 placed. Wash the asbestos thoroughly with hot water and 

 then with 10 c.cms. of alcohol followed by 10 c.cms. of ether. 

 Dry for thirty minutes in the steam oven and weigh. The pre- 

 cipitate of cuprous oxide is collected as above, washed with 

 water, treated with 10 c.cms. of alcohol and ether, successively, 

 and dried for thirty minutes at 100 C. The weight of Cu20 

 multiplied by 0.8883 gives the weight of metallic copper. 



PKOTEIDS 



Total Proteids. 5 gms. of milk are placed in a Kjeldahl 

 flask of about 150 c.cms. capacity and 20 c.cms. of pure cone, 

 sulphuric acid added. The mixture is heated over a small flame 

 until excessive frothing has ceased, and after cooling, 8-10 grms. 

 of acid potassium sulphate and a drop of mercury are added. 

 After placing a sealed funnel containing water in the mouth 

 of the flask to prevent excessive evaporation, the contents of 

 the flask are gradually heated and the flame slightly increased 

 as frothing ceases. When the liquid becomes colourless the 

 flask is allowed to cool and the contents washed with the aid of 

 distilled water into a flask. This flask should be provided 

 with a stopper having two holes, one containing a trapped bulb 

 tube connected with a water condenser, and the other a tapped 

 funnel reaching almost to the bottom of the flask. After the 

 contents of the Kjeldahl flask have been transferred, a few pieces 

 of- pumice, unglazed porcelain, or granulated zinc, are added 

 to prevent bumping and the distillation apparatus connected 

 up with the outlet of the condenser dipping into a beaker con- 



N 

 taining 50 c.cms. of - acid. Through the funnel add 100 c.cms. 



