160 



ElletCs method applied to Fucus vesiculosis. 

 [Two grams of material.] 



BEST RESULTS BY WASHING WITH HOT ALCOHOL. 



THE DETERMINATION OF ACIDITY IN CATTLE FEEDS. 

 By JOHN PHILLIPS STREET, Referee. 



The acidity of a cattle food is due to the presence of hydrogen ions. In a solution 

 containing a mixture of salts of organic and inorganic acids it makes practically no 

 difference whether this acidity was originally produced by the addition of a small 

 amount of an organic or of an inorganic acid, for the final result is essentially the same; 

 that is, the presence of a certain proportion of free hydrogen ions and of the ions of all 

 the various salts which are present in the solution. The question of acidity, there- 

 fore, is one of degree rather than of kind and, from a physiological view point, depends 

 on the nature of the salts which are present in the solution under consideration. Let 

 us take an example. We have a solution containing sodium chlorid and sodium 

 acetate. In this we have sodium ions, chlorin ions, acetate ions, undissociated sodium 

 acetate molecules, and undissociated sodium chlorid molecules. If a small quantity 

 of hydrochloric acid is added to this solution it will then contain, in addition to the 

 substances above named, a certain quantity of hydrogen ions and a correspondingly 

 greater quantity of chlorin ions. If a molecularly equivalent quantity of acetic acid 

 is added instead of hydrochloric, the solution will contain the hydrogen ions, as in the 

 first case, and the number of acetate ions will be correspondingly increased. 

 If we now measure the acidity of each of these two solutions with phenolphthalein 

 as an indicator, the result will be the same, for this indicator gives a pretty accurate 

 measure of free and potentially free hydrogen ions. If we measure the acidity of these 

 solutions by means of delicate litmus paper the degree of acidity will be found to be 

 less than that as determined by phenolphthalein. The reason for this is to be found 

 in the fact that litmus is a relatively stronger acid than phenolphthalein and reacts 

 with the base before all the acid hydrogen of the acetic acid has been acted on. The 

 effect of the presence of organic salts is to reduce the number of free hydrogen ions, 

 in comparison with that which would be present in a solution to which had been added 

 the same quantity of mineral acid in the presence simply of inorganic salts of strong 

 bases with strong acids, such as sodium chlorid or sodium sulphate, and it is also clear 

 that it is not possible to determine in a solution containing a mixture of organic and 

 inorganic salts, which show an acid reaction, whether this reaction was originally 

 caused by the action of a mineral acid or of an organic acid. The indicators that are 

 commonly supposed to distinguish between mineral and organic acids in mixtures 



