LACTOMETER 33 



manufacture of these foils is, I believe, quite an art, and formerly there was only one 

 person in Birmingham who knew how to practise it successfully.' Percys Metallurgy. 



LACTIC ACID, C 12 H 12 12 (C 6 H 12 6 ). Syn. Nanceic acid. (Atide lactique, Fr. ; 

 Milchsaure, Ger.) Discovered by Scheele in sour milk. Subsequently, M. Braconnot 

 examined the sour liquid which floats above starch during its manufacture, also the 

 acidified decoctions of various vegetables, including beet-root, carrots, peas, &c., and 

 found an acid which he considered to be peculiar, and consequently named the nanceic. 

 The acid formed under all these circumstances turns out to be the same ; it is, in fact, 

 lactic acid, which modern researches show to be a constant product of the fermentation 

 of sugar, starch, and bodies of that class. The acidity of sauerkraut is due to the 

 presence of the same substance. Liebig extended and confirmed the experiments made 

 many years ago by Berzelius, on the presence of lactic acid in the juice of flesh, but 

 he denied its existence in urine, as asserted by MM. Cap and Henry, and others. 



Preparation. Lactic acid can be prepared easily in any quantity by the fermenta- 

 tion of sugar. Care must be taken, however, that the process does not go too far, 

 because lactic acid undergoes with facility another decomposition, by which it becomes 

 converted into butyric acid. The following process of M. Bensch for the preparation 

 of lactate of lime can be recommended by the author of this article as yielding at a 

 small trouble and expense a very large quantity of product. In fact, he has prepared 

 with facility upwards of 3 pints of butyric acid from lactate of lime obtained in this 

 manner. Dissolve 6 Ibs. of lump-sugar, and oz. of tartaric acid in 2J gallons of 

 boiling water. Leave for a day or two, and then add 2 oz. of rotten cheese, and a 

 gallon of skimmed milk stirred up with 3 Ibs. of well-washed prepared chalk. The 

 temperature should not fall below 86 F. nor rise above 95. The water lost by 

 evaporation must be made up by adding a little every few days. After a time, vary- 

 ing from 10 days to a month, according to the temperature and other circumstances, 

 the whole becomes a magma of acetate of lime. Two gallons of boiling water must 

 then be added, and oz. of quicklime, and the whole, after being boiled for half an 

 hour, is to be filtered through a linen or flannel bag. The filtered liquid is to be 

 evaporated until it begins to get somewhat syrupy, the fluid in this state being put 

 aside to allow the salt to crystallise. The crystals, after being slightly washed with 

 cold water, are to be recrystallised two or three times. To obtain lactic acid from the 

 lactate of lime, it is necessary, in the first place, to convert the latter salt into that of 

 zinc. For this purpose a crude lactic acid is first obtained thus : to every 2 Ibs. 3 oz. 

 of lactate of lime dissolved in twice its weight of boiling water, 7 oz. of oil of vitriol 

 previously diluted with twice its volume of water are to be added. The boiling fluid 

 is to be strained through a linen bag to remove the precipitate of gypsum, and the 

 filtered liquid is to be boiled for 15 minutes with 8| oz. of carbonate of zinc. The 

 boiling must not be continued longer, or a subsalt of sparing solubility would be pro- 

 duced. The liquid, which is to be filtered boiling, will deposit on cooling the lactate 

 of zinc in colourless crystals, which are to be washed with a little cold water, and after 

 being drained are to be dried by exposure to the air on frames covered with filtering 

 paper. The mother-liquid will yield a fresh quantity of lactate if it be boiled with 

 the salt remaining on the filter and evaporated. 



From the lactate of zinc the acid is to be separated by passing sulphuretted 

 hydrogen through the solution of the salt in eight times its weight of boiling water. 

 The gas is to be expelled by heat, and the fluid on evaporation yields pure syrupy 

 lactic acid. 



Lactic acid is a colourless syrupy liquid of a powerful pure acid taste. Its specific 

 gravity is 1-215. It is bibasic. 



The most important salts of lactic acid are those of zinc and lime. The former salt 

 is that generally formed in examining animal or vegetable fluids with a view to the 

 isolation of the acid. It is found with two different quantities of water according to 

 the circumstances under which it is prepared, and it is worthy of remark that the 

 amount of water of crystallisation remarkably affects the solubility of the salt in water 

 and alcohol. 



All the butyric acid employed for the preparation of butyric ether, or pine-apple 

 essence, is now prepared by the fermentation of lactate of lime. C.G.W. 



liACTOMETER is the name of an instrument for estimating the quality of 

 milk, called also a Galactometer. The most convenient form of apparatus would be 

 a series of glass tubes each about 1 inch in diameter, and 12 inches long, graduated 

 through a space of 10 inches, to tenths of an inch, having a stopcock at the bottom, 

 find suspended upright in a frame. The average milk of the cow being poured in to the 

 height of 10 inches, as soon as the cream has all separated at top, the thickness of its 

 body may be measured by the scale ; and then the skim-milk may be run off below 

 into a hydrometer glass, in order to determine its density or relative richness in caseous 

 matter, and dilution with water. 



VOL. III. D 



