123 



IlaSO^, and finally extracting with ether. One hundred grams of water- 

 free crystals of the acid were obtained in this manner. This acid 

 agreed with i)ure (;itricacid in (1) elementary composition; (li) the ability 

 to form a saturated sodium salt giving no acid reaction with phe- 

 nolphthalein; (.J) water of crystallization of the calcium salt and the 

 Ix'havior of this when the salt was dried over H,.S(),, or at 100'^ C; (4) 

 the calcium content of the saturated (tri) and unsaturated (di) calcic 

 salt; (5) melting point; (6) solubility in ordinary solvents; and (7) giving 

 the Sabanin-Laskowski reaction, which is peculiar to citric and acouitic 

 ai'ids only. 



Experiments were next made to determine whether the citric acid 

 was actually conraine<l in the milk, or whether it was possibly forn)ed 

 during the i)rocess of preparation from a decomposition of the constitu- 

 ents of the milk, either by the rennet or by the continued evaporation 

 of the serum. Serum j)repared from fresh cows' milk without the use 

 of rennet, (!) by means of Ht^l, etc., and (2) by filtering the milk 

 through cells of unglazed earthenware and heating, yielded in both 

 cases an organic acid with the characteristics given above. San)i)les 

 of serum prepared in each of the three ways (with and without rennet) 

 were rai)idly evaporated in a vacuum at 4:(P (J. ; all yielded the same 

 amount of calcium citrate found in previous trials. These results showed 

 conclusively that the citric acid found was not a product of the decom- 

 ]»osition of the milk constituents by the rennet or by the continued 

 heating of the serum. It must therefore be a constituent of the niilk 

 used in the investigations. 



Finally, 30 samples of milk from different herds of cows receiving 

 dill'erent rations, and the mixed milk from creameries, were examined 

 with reference to their citric-acid content. The amount of calcium salt 

 found (containing only a trace of calcic phosphate) varied from 1.5 to 

 li. 1 grams, equivalent to from 1 to 1.4 grams of citric acid per liter of 

 milk. Numerous examinations made of the concretions an<l sediment 

 forming in sterilized and unsterilized condensed milk, showed these 

 materials to consist to considerable extent of calcium citrate. 



The results of these investigations lead the author to conclude that 

 citric acid is regularly present and a normal ingredient of cows' milk. 



Concerning the origin of citric acid in milk, A. Scheibe {f.andw. 

 Vers. Stat.j 3{),pp. 153-170). — This investigation, like the preceding, was 

 made in the laboratory of the Central Experiment Station at ^Munich, 

 under the supervision of Professor Soxhlet. The questions proposed 

 by the author were: (1) Is citric acid contained in other than cows' 

 milk? and (2) From what source does the citric acid in milk comet In 

 aprelimiiuiry report on the investigations of Henkel, Professor Soxhlet 

 stated that no citric acid had been found in human milk, and he 

 suggested that its presence in the milk of herbivora might perhaps be 

 accounted for in two ways: (1) Citric acid being a constituent of vege- 

 table foods, as hay, roots, etc., may pass from the food into the milk; 



