60 THE BUTYRIC ACID GROUP. 



oxygen =300). Now if, in a baryta-salt, we have found 49 of 

 baryta and 51% of butyric acid, then 49 : 51 must be the ratio in 

 which the known atomic weight of baryta (=955*3) stands to the 

 atomic weight of butyric acid (49 : 51 : : 955*3 : x)= 994*4. 



By a similar determination of the quantity of a base contained 

 in a salt, we calculated the saturating capacity, by which, as is 

 well known, we understand the number which expresses the quan- 

 tity of oxygen contained in that quantity of base which is required by 

 100 parts of an anhydrous acid to form a neutral salt. Hence the 

 saturating capacity of butyric acid is = 10*126. If we regard the 



above instance as an empirical result, 49 BaO saturate 51 Bu, or 



100 Bu saturate 96*076 BaO; in this, however, there are con- 

 tained 10*06 parts of oxygen, which is a tolerably close approxi- 

 mation to the required number. 



Physiological Relations. 



Occurrence. In the contents of the stomach, or rather in food 

 which has been ejected by vomiting, we sometimes meet with a 

 nauseous acrid or rancid-smelling volatile acid, which, beyond all 

 question, is butyric acid. Tiedemann and Gmelin often obtained 

 a fluid resembling butyric acid by distillation of the contents of the 

 stomachs of sheep, oxen, and horses, fed with oats. Since the con- 

 tents of the stomach can pass into the acetous, and, as we shall 

 presently see, also into the lactic fermentation, there is nothing 

 surprising in the circumstance of their also passing into the 

 butyric fermentation : but even in abnormal conditions, butyric 

 acid has not been recognised in the contents of the stomach with that 

 absolute certainty which is as necessary in physiologico-chemical 

 researches as in all other departments of natural enquiry. 



Free butyric acid was long ago discovered in the urine by Ber- 

 zelius, who, however, did not think that it was often to be found 

 there. In the urine of pregnant women, and of those who, after 

 delivery, do not suckle their children, I have sometimes found 

 butyric acid, or, at all events, a fat which, on saponification, yielded 

 a volatile acid, with the odour of butyric acid. 



In the sweat, especially in that of the genitals and lower extre- 

 mities of corpulent persons, we find volatile matters, with an acid 

 reaction, and having an odour partly of butyric acid and partly of 

 other acids of this group. Berzelius thought that the acid reaction 

 was due to butyric acid alone, but in the present state of our 

 knowledge it must remain doubtful whether the homologous, highly 



