258 THE BLOOD. [CH. X. 



of starch solution. The iodate yields free iodine owing to the 

 presence of the acid in the coagulating fluid. The mixture is then 

 titrated with standard silver till the blue colour disappears. From 

 the amount of silver required to effect this, the amount of silver in 

 the filtrate can be determined. Thus the amount of silver that has 

 disappeared in the formation of silver chloride can be calculated, 

 and so the amount of chloride in the blood taken. 



Preparation of reagents. 



1. N/ioo silver nitrate. 1-7 gram, of pure silver nitrate are dissolved in 

 distilled water and the volume made up to i litre. It should be stored in a 

 dark bottle and kept in the dark. 



2. Iodide andiodate solution. 0-015 gram, of potassium iodate and i -7 gram, 

 of potassium iodide are dissolved in water and the volume made up to i litre. 

 2 cc. of the solution are measured and treated with 10 cc. of solution 3 and a 

 few drops of the soluble starch. This mixture is titrated with N/ioo silver 

 nitrate from a microburette until the blue colour disappears. The strength 

 of the solution must be adjusted by the addition of water or of a dilute solution 

 of potassium iodide until 2 cc. require exactly 2 cc. of the silver nitrate. 



3. Acid magnesium sulphate. 2 litres of a 30 per cent, solution of 

 magnesium sulphate, 120 cc. of strong pure nitric acid (sp. gr.i'42) and 280 cc. 

 of distilled water are mixed. 



4. Starch solution, i gram, of soluble starch are suspended in a little cold 

 water and poured into about 80 cc. of boiling distilled water. 20 grams, of pure 

 potassium nitrate are added to the mixture. The solution is poured into a 

 number of small sterile bottles and stoppered whilst still hot. In this way the 

 solution can be preserved for a considerable time. 



5. Kieselgur. This should be purified by heating to a dull red, washing 

 with 10 per cent, acetic acid and then with distilled water and heating again 

 to redness. 



Measure 0-2 cc. of distilled water into a tube about 5 cm. in length and 

 about 5 mm. bore which has one end sealed. Make a mark with a file or a 

 label to show the height of the fluid. Dry the tube thoroughly. The amount 

 of kieselgur for each experiment is measured by filling the tube to the mark 

 after gently tapping. 



Since kieselgur adsorbs silver nitrate it is essential to determine the 

 amount of this for every specimen by a blank experiment conducted as 

 follows : To 10 cc. of solution 3 add 2 cc. of the silver nitrate and the measured 

 amount of kieselgur. Shake and filter through a Gooch crucible as described 

 below. Wash the tube and the kieselgur twice with 5 cc. of distilled water. 

 To the filtrate add 2 cc. of the solution 2 and a few drops of the starch solution. 

 Titrate cautiously with N/ioo silver nitrate from a microburette till the blue 

 colour is discharged. The amount of silver required corresponds to the 

 amount adsorbed by the kieselgur. 



Method of Analysis. 



i. To obtain a measured amount of blood. The procedure 

 is exactly the same as described in the section on the micro-analysis 

 of sugar (p. 254). 



