CH. IV.] 



GLYCINE. 



75 



(ix.) Cool the filtrate, first under the tap, and then with ice, and 

 pass in a stream of dry hydrochloric acid gas (see fig. 10) 

 until the fluid is saturated. 



Fig. 10. Apparatus for saturating a fluid with dry 

 hydrochloric acid gas. 



B is concentrated hydrochloric acid. A is concentrated sulphuric^acid, 

 which is allowed to drop slowly into the flask. C contains concentrated 

 sulphuric acid to dry the gas. The dry gas can be introduced into the 

 fluid by means of a Folin absorption tube, D, though this is not usually 

 necessary. 



(x.) Boil on a water bath under a reflux condenser for 30 minutes, 

 cool thoroughly, and allow it to stand over-night in a 

 refrigerator. The glycine ester hydrochloride generally 

 separates as a mass of colourless needles. Should this 

 not occur, it is advisable to " sow " the fluid with a 

 small quantity of the crystals obtained from another 

 preparation, or rub the sides of the vessel with a 

 glass rod. [A second crop of crystals can often be ob- 

 tained by concentrating in vacuo and repeating processes 

 (ix.) and (x.)]. 



