161 



containing *lUoi w.-ak buefl and strong acids, or of strong bases and weak acids, give 

 entirely different results from those obtained in solutions free from such salts, for by 

 hydrolytic dissociation these salts contribute to the solution a certain quantity of 

 hydro-,-!! '>r hydn.xyl ions, according to the nature of the salts present and the con- 

 centration .! the solution, which ions exert an effect on the indicator in one direction 

 or the other. 



In u mixturv of weak and strong acids and their salts, phenolphthalein, which is the 

 \\vake.-t indicator commonly employed, gives the total amount of acids present 

 Htnmii.T than phenolphthalein, itself an exceedingly weak acid. If a stronger acid 

 indicator, e. g., litinue, is in the above mixture, it will appear to have less total acid, 

 because the litmus itself reacts with the base before the weaker acids are acted on. 



It is thus clear that, for such a mixture, it is impossible to determine the acidity 

 of it> solution, and, furthermore, it is not even possible by titration to determine the 

 actual concentration in free hydrogen ions, which, from a physiological standpoint, 

 i.- tin- true question under consideration. 



h has been th- practice >f physical chemists to determine the concentration in 

 hydrogen ions by inverting cane sugar, a process which closely corresponds with the 

 enzym reaction.- i physiological processes. 



The acidity of a . attic feed may come from a mineral acid used in its preparation, 

 from ..r_Miiic .Hid- natural to the product itself, or developed by fermentation during 

 it- preparation, and poewihly, in some cases, from phosphates having an acid reaction 

 and normally present in the feed. 



Jordan'- .-tudie- Bulletin i.':>s, (ieneva station), however, indicate that "our com- 

 IIHTI i.d feed- of vegetable iiu'in do not contain appreciable quantities of phosphorus 

 in inorganic combination." 



l-'.n-ilaL'e i- .in example of a feed containing considerable amounts of organic acids 

 de\. -loped in the -il. i by fermentation. A n urn her of other feeds which are by-products 

 of manufacturing processes contain organic acids resulting, likewise, from fermenta- 

 akiiiir place diirini: manufacture. 



In \ ie\\ of the net that the presence of free mineral acids in certain feeds has been 

 'ted or allirmed, I wish to raise the question of the methods involved and ask 

 the a.-s.K-iation to make it the subject of inquiry, in order that an accurate method of 

 te-tin- for acidity may In- found and adopted. As matters now stand, we are depend- 

 in- \\holly on volumetric methods and the use of indicators, and the question to be 

 settled first of all is. .Ju.-t what do indicators indicate? 



little attention has Keen ,MVIMI to the acidity due to the proteins themselves and 

 their varying action with different indicators. Osborne has pointed out that the 

 pfOteinc are Dot neutral hodies, like the carbohydrates, and that the general assump- 

 tion that u solution containinu' protein matter, and showing neither acid nor alkaline 

 with litmus, is chemically neutral, is erroneous. Many experiments have shown that 

 certain protein solutions, when neutral to litmus, are acid to phenolphthalein and 

 alkaline to lacmoid It ha- also been established that a notable amount of acid can 

 Ulded to a protein solution before an acid reaction with tropaeolin, alizarin, or 

 phloro^lucin and vanillin is given. 



A - ( )sborne says, b it is of importance "to know whether litmus can be used to deter- 

 mine the point when all combined acid has been converted into neutral salts of potas- 

 sium or sodium and all the protein substance has been set free, or whether, as we know 

 i- i he case, when tropaeolin or lacmoid is used as an indicator, more acid still remains 

 combined ' 



A.pieous solutions of crystallized ovalbumin, solutions in sodium chlorid brine of 

 ex. -elsin. amandin, vignin, conglutin, glycinin, corylin, phaseolin, and legumin, and 

 solution, ,,f /, n,, -riiadin, and hordein in 75 to 90 per cent alcohol, which were either 



" J. Amer. Them. So,-., 1902, 24: 39. b Loc. cit. 



7. : 173 Bull. 12209 - 11 



