288 PHYSIOLOGICAL CHEMISTRY 



4 c.c. of Solution III. On adding Solution III a slight turbidity appears, which in 

 no way interferes with the end point. 



The potassium iodide solution is then run in from a burette until the blue end 

 point appears. The first definite blue color is taken as the end point, and with 

 slight practice is unmistakable. An additional drop, which may be used as a control, 

 causes such a deep blue color that it is impossible to make an error of more than one 

 drop in titratipn. Should the end point be accidentally passed, one may add i c.c. 

 of Solution I, i c.c. of Solution III and retitrate, allowing in the calculation for the 

 extra silver nitrate. 



The result may be calculated from the following formula, which applies only 

 when 20 c.c. of the nitrate from silver chloride are titrated: 



12.5 (8 c.c. KI solution used) 

 Grams NaCl per liter* c . c . blood filtrate taken 



Thus, if 13 c.c. of filtrate are obtained and titrated after precipitation of plasma 

 protein, and 1.60 c.c. of KI are used in the final titration, 



Grams NaCl per liter = - - = 6.15. 



In case only i c.c. of plasma instead of 2 c.c. has been used, the factor 25 replaces 

 12.5 in the numerator. The error should be within a limit of i per cent. 1 



ii. Total Solids. The total solids of the blood are most readily determined by 

 using a type of weighing bottle differing from the usual form merely in having a 

 glass loop attached to the under side of the stopper. 2 A block of filter paper is 

 suspended from this loop by means of a small wire hook. The bottle and filter 

 block are dried and weighed. From a small pipette 0.3-0.6 gram of the well-mixed 

 blood is allowed to flow rapidly upon the filter block. The stopper is quickly 

 inserted and the bottle weighed. The stopper is then tilted and the bottle placed 

 in the drying oven at 105 over night. When convenient the bottle is cooled and 

 again weighed. The total solids are calculated from the loss of moisture. 



12. Relative Hydrogen Ion Concentration of the Blood. Method 

 of Levy, Rowntree, and Marriott. 3 Principle. The blood is dialyzed 

 against normal salt solution and the H ion concentration of the protein- 

 free dialyzate is determined by the indicator method, using phenol- 

 sulphoneph thalein . 



Procedure. One to 3 c.c. of clear serum or of blood is run, by means of a 

 blunt-pointed pipette, into a dialyzing sac 4 which has been washed outside and 



1 The exactness of the method depends directly on the care with which measurements 

 are made and on the purity of the reagents used. All reagents must, of course, be free 

 from substances precipitated by silver, and are easily tested. As the volumes measured 

 are not large, however, small absolute errors in measurement may cause considerable 

 percentage error in the final result. All glassware must therefore be carefully calibrated 

 by either the weight of water contained (flasks, cylinders, 2 c.c. pipettes) or the weight de- 

 livered (other pipettes, burettes), and burettes should be used which are capable of being 

 read to 0.02 c.c. and which deliver small drops. If these precautions are followed, one 

 should uniformly obtain results, which are well within a limit of error of i per cent. 



2 Myers and Fine: "Chemical Composition of the Blood in Health and Disease," 

 1915. The weighing bottles may be obtained from Eimer and Amend, N. Y. 



3 Levy, Rowntree and Marriott, Arch. Int. Med., 16, 389, 1915. 



4 Preparation of Sacs. One ounce of celloidin is dissolved in 500 c.c. of a mixture of 

 equal quantities of ether and ethyl alcohol. The solids swells up and disolves with oc- 



