290 PRACTICAL PHYSIOLOGY 



rate (not quicker than 5 c.c. per minute). 1 The flask must not be 

 moved until after the end of an hour, when it is shaken and the pre- 

 cipitate collected on an asbestos mat in a Gooch crucible, washed with 

 about 250 c.c. cold water, then with alcohol and ether, dried and ignited. 

 In doing this, the flame must not be applied directly to the perforated 

 bottom of the crucible, but the Gooch crucible must be placed in a 

 large nickel crucible. The crucible must also be covered with a lid 

 during the ignition. Ten minutes' ignition is usually sufficient ; 

 precipitate should be quite white. Cool and weigh. 



Total Sulphates (Inorganic and Ethereal) (Folin). 25 c.c. urine 



are mixed with 20 c.c. of dilute hydrochloric acid (1:4) in an 

 Erlenmeyer flask of about 250 c.c. capacity, and, after covering the 

 mouth of the flask with a watch-glass in a small filter funnel, 

 gently boiled for twenty to thirty minutes. The flask is then cooled 

 in running water, its contents diluted with distilled water to about 

 150 c.c. and 10 c.c. of 5 per cent, solution of barium chloride added, 

 and the further procedure followed as above described. 



BaSO 4 : S = 1 : 0-1374 ; BaSO 4 : SO 3 = 1 : 0-3429. 

 Total sulphates inorganic sulphates = ethereal sulphates. 



Total Sulphur. Modified Benedict Method (Denis). Place 10 c.c. 

 of urine in a small (about 7 cm. diam.) porcelain evaporating basin 

 and 5 c.c. of copper nitrate reagent (125 gms. copper nitrate (sulphate 

 free) ; 125 gms. sodium chloride ; 50 gms. ammonium nitrate : distilled 

 water to 500 c.c.). Evaporate on the waterbath (or over a very small 

 flame) to dry ness. When quite dry heat the residue gently with a 

 small flame until it is blackened. The flame is then gradually increased 

 and the basin is heated to redness for ten minutes after the black 

 residue, which first fuses, has become dry. Allow the basin to cool, 

 add 1020 c.c. dilute HC1, and warm gently till complete solution of 

 the contents takes place. Transfer to a beaker, dilute with cold water 

 to 100-150 c.c., add 10 c.c. 10 per cent. BaCl 2 solution and continue 

 as in the sulphate estimations. 



Total sulphur less total sulphates = neutral sulphur. 



If special accuracy is required an alcohol flame must be used for 

 heating instead of gas as gas contains much sulphur and may thus 

 give too high results. 



Volumetric Method of Estimating Sulphates. (Rosenheim and 

 Drummond's benzidine method.) 



This method depends upon the insolubility of benzidine sulphate 

 in hydrochloric acid solution. Ethereal sulphates may be determined 

 by this method after hydrolysis of the ethereal sulphates by hydro- 

 chloric acid as in the Folin determination. Total sulphates less 

 inorganic sulphates = ethereal sulphates. 



20 c.c. of urine are placed in a 250 c.c. flask and acidified with dilute 

 HC1 (1:4) until the reaction is distinctly acid to Congo red, then 

 100 c.c. of benzidine 2 solution is run in. A precipitate forms in a 

 few seconds, and after standing ten to fifteen minutes it is filtered 

 under pressure, care being taken not to allow the precipitate to be 



1 More rapid addition of the reagent causes the results to be too high, i.e. 

 produces an impure precipitate. 



2 Benzidine solution. Rub 4 gms. of benzidine into a paste with water, 

 transfer it with about 500 c.c. water into a 2 litre flask. 5 c.c. cone. HC1 

 ere added and the volume made up to 2,000 c.c. with water. 



