EXPERIMENT STATION BULLETINS. 



617 



From the results of this titration, the amount of ammonia necessary 

 to bring the whole volume of the acid citrate solution up to the same 

 reaction can be calculated. After the addition of the calculated quantity 

 to the bulk of the solution its reaction is checked by transferring a 

 few cc. to a test tube, diluting to the same volume as that of the standard 

 and comparing their colors after the addition of the proper quantity 



to 



IS 



brought 



of indicator. If they check, the density of the solution 

 1.09 at 20° and if desired, the reaction again checked. 



It is a well known fact which has already been referred to in this 

 article that the hydrogen ion concentration of a solution is altered 

 by its dilution, the extent of the change depending on several factors. 

 A number of tests demonstrated, however, that ammonium citrate solu- 

 tions of the concentrations met with may be diluted at least five times 

 without undergoing a noticeable change in reaction. We have never 

 been able, for instance, to detect a change in the reaction of a solution 

 which had been adjusted as outlined above, upon diluting it to the 

 required density of 1.09, though the test was always repeated after this 

 dilution. 



The accuracy with Avhich duplicate titrations may be made is shown 

 by the following results. A solution of ammonium citrate was prepared 

 having a reaction corresponding to a Ph of G.7. Three 10 cc. samples, 

 titrated independently i. e. Avithont observing the burette until after the 

 end of each operation, required respectively 12. Go, 12.68 and 12.68 cc. 

 2^\/10 NH.OH to give a reaction of 7.4. 



A similar experiment with another solution gave values 

 and 6.37 cc. N/IO NH^OH to raise the reaction of a 10 cc. 

 Ph of 7.0. 



When an attempt was made to use a sample of litmus 

 origin and Hand's technic, no ditTerence in tint could 

 between the sample and the standard neutral color, though there was 

 a very decided difference with plienol red between the color of this 

 solution and the Clark and Lubs standard with a P h of 7.0. Upon 

 substituting some Kahlbaum's "Al" litmus for that used above, the 

 following figures were obtained for as many successive and independent 

 titrations with 10 cc. samples: 



of 6.32, 6.32 

 sample to a 



of unknown 

 be observed 



1. 



9 



o 

 o. 



4.17 cc. N/10 KH.OH 



4.67 cc. N/10 NH.OH 



3.82 cc. K/10 NH.OH 



4.72 cc. N/10 NH.OH 



The results with Kahlbaums azolitmin were no better: 



1. 4.70 cc. N/10 NH.OH 



2. 5.00 cc. N/10 NH.OH 



3. 4.00 cc. N/10 NH.OH 



4. 4.00 cc. N/10 NH.OH 



It Avas difficult to get a perfect match witli the two sets of tubes and 

 the color change upon the addition of a small quantity of the alkali 

 was insignificant. 



Using Clark and Lubs standards, azolitmin as indicator and the technic 

 described for the use of phenol red, somewhat better j-esults were 

 obtained. 



