362 SARCOLACTIC ACID LACTIC ACID OF FERMENTATION. [BOOK I. 



raw acids is dissolved in water and boiled with suspended zinc carbonate or 

 zinc oxide ; the clear liquid is separated by filtration from the insoluble 

 zinc compounds, and then evaporated until crystals commence to form. 

 The liquid is now treated with four or five times its volume of 90 per cent, 

 alcohol; after some time the liquid becomes turbid and deposits needle- 

 shaped crystals, consisting of zinc sarcolactate ; the ethylene-laetate, being 

 far more soluble in alcohol, remains in solution. The crystals of the former 

 body are then collected on a filter, washed with cold absolute alcohol; and 

 they may with advantage be re-crystallized. From the zinc compound 

 sarcolactie acid may be obtained by dissolving the salt in water, decompos- 

 ing by means of sulphuretted hydrogen, filtering the solution, concentrating, 

 shaking with ether, and then evaporating the ethereal solution, when the 

 pure acid is left. 



Properties Sarcolactie acid is distinguished from the two other 



of sarcolactie varieties of lactic acid by its property of deviating the plane 

 acid and its of polarization to the right. The specific rotatory power is 

 compounds. greatest immediately after the acid is dissolved; it then 

 sinks rapidly, and afterwards slowly rises again, without however again 

 reaching its initial value. It is worthy of note that whilst free sarcolactie 

 acid is dextrogyrous, its salts are laevogyrous. 



Zinc sarcolactate has the composition Zn (C 3 H 5 O 3 ) 2 + 2H 2 0. When 

 heated for half an hour at 100 C. it loses the whole of its water of crystal- 

 lization (12-9 per cent.). It is soluble in 17'5 parts of water at 14 15 C. 

 It is almost insoluble in absolute alcohol, requiring 1000 parts of boiling 

 absolute alcohol for solution. 



x 



The specific rotation of this salt is =- 7'6. 



Calcium sarcolactate, 2 [Ca (C 3 H 5 3 ) 2 ] + 9H 2 O, crystallizes in the form 

 of tuits of microscopic needles. The specific rotation of the salt is = - 3 '8. 



b. Ordinary Lactic Acid. (Optically inactive ethylidene lactic acid.) 



This acid is perhaps not present in acid muscle, though it has been stated 

 to be so by Heintz. Its quantity is at least inferior to that of the other 

 isomeric lactic acids. 



Preparation. This acid is formed when saccharine liquids ferment in 

 the presence of certain decomposing matters of animal origin (Milk, Cheese), 

 which serve as vehicles for a peculiar organized ferment ; to the fermenta- 

 tion thus induced the term lactic acid fermentation is applied. For this 

 reason this variety of lactic acid is often designated 'lactic acid of fermenta- 

 tion.' For the details of the methods for preparing this variety of lactic 

 acid the reader is referred to any systematic work on organic chemistry. 



The acid resembles sarcolactie acid except in its not 

 of inactive possessing the power of rotating the plane of polarization, 



ethylidene Its salts differ in crystalline form and in the amount of water 



lactic acid o f crystallization which they contain, from those of sarcolactie 



and its com- add> 



Zinc lactate has the composition Zn (C 3 H 5 3 ) 2 + 3H 2 O. 

 When heated in the water-bath for half an hour it loses all its water 



