PHYSIOLOGICAL CHEMISTRY 



tinuously. Filter (reserve the filtrate) , and press the precipitate as dry as possible 

 between filter papers. Open the papers and allow the ether to evaporate spon- 

 taneously. Grind the precipitate to a powder in a mortar. Upon the casein 

 prepared hi this way make the following tests : 



(a) Solubility. Try the solubility in water, sodium chloride, dilute acid and 



alkali. 



(b) Millon's Reaction. Make the test according to the directions given on 



page 97. 



(c) Biuret Test. Make the test according to directions given on page 98. 



(d) Glyoxylic Acid Reaction (Hopkins-Cole). Make the test according to 

 the directions given on page 98. 



(e) Unoxidized Sulphur. Test for unoxidized sulphur according to the di- 

 rections given on page 108. The sulphur content of casein is rather low, e.g., 

 about 0.7 per cent. 



(f ) Fusion Test for Phosphorus. Test for phosphorus by fusion according to 

 directions given on page 129. Casein contains 0.7 per cent of phosphorus. 



15. Coagulable Proteins of Milk. Place the filtrate from the original casein 

 precipitate hi a casserole and heat, on a wire gauze, over a free flame. As the 

 solution concentrates, a coagulum consisting of lactalbumin and lactoglobulin 

 will form. Continue to concentrate the solution until the volume is about one- 

 half that of the original solution. Filter off the coagulable proteins (reserve the 

 filtrate) and test them as follows : 



(a) Millon's Reaction. Make the test according to the directions given on 



page 97. 



(b) Biuret Test Make the test according to the directions given on page 98. 



(c) Glyoxylic Acid Reaction (Hopkins-Cole). Make the test according to 

 the directions given on page 98. 



16. Detection of Calcium Phosphate. Evaporate the filtrate from the 

 coagulable proteins, on a water-bath, until crystals begin to form. It may be 



necessary to concentrate to 15 c.c. before any crys- 

 tallization will be observed. Cool the solution, filter 

 off the crystals (reserve the filtrate), and test them 

 as follows : 



(a) Microscopical Examination. Examine the 

 crystals and compare them with those in Fig. 105. 



(b) Dissolve the crystals in nitric acid. Test 

 part of the acid solution for phosphates. Render 



FIG. 105. CALCIUM the remainder of the solution slightly alkaline with 

 ammonia, then acidify with acetic acid and add am- 

 monium oxalate. Examine the crystals under the microscope and compare 

 them with those in Fig. 134, page 459. 



17. Detection of Lactose. Concentrate the filtrate from the calcium phos- 

 phate until it is of a syrup-like consistency. Allow it to stand over night and 

 observe the formation of crystals of lactose. Make the following experiments. 



(a) Microscopical Examination. Examine the crystals and compare them 

 with those in Fig. 104, page 318. 



(b) Fehling's Test. Try Fehling's test upon the mother liquor. 



(c) Phenylhydrazine Test. Apply the phenylhydrazine test to some of the 

 mother liquor according to the directions given on page 22. 



