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 ccm^s. of alcohol and ether, successively, 

 and dried for thirty minutes at 100° C. The weight of CU2O 

 multipHed by 0.8883 gives the weight of metallic copper. 



Peoteids 



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 hquid 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. 



