76 ALCOHOL.—:
Glycerine (C 3 II s 0 3 ) may be detected in almostthe same way, but in place of ether it is better toexhaust the residue with a mixture of alcohol andether. This mixture dissolves the succinic acid andglycerine, and leaves behind the nitrogenized matter.The ethereal and alcoholic solution is concentrated,saturated with lime, and then evaporated to dryness.The residue is again treated with the mixture ofalcohol and ether, which now only dissolves theglycerine, and leaves the succinate of lime.
When it is wished to isolate the succinic acid andglycerine completely, and determine them quantita-tively, it is necessary to adopt particular precautions.The principal difficulty in the analysis of a fermentedliquid proceeds from the soluble products whichthe yeast supplies, or which result from its transfor-mations. The nature of these products is alwaysthe same, but their proportion varies with thequantities of yeast and sugar employed.
When yeast is mixed with a solution of sugar itgives up to that liquid a part of the soluble principlesconfined in the interior of its globules. Some salinematters, principally phosphates, and some nitro-genous albumenoid matters are dissolved, and theglobules deriving part of their nourishment fromthese two sorts of substances,‘live, bud, and multiply.These mutations give rise to modifications of theoriginal products, or to new bodies, some solid andinsoluble, others liquid and soluble, which remain inthe liquid, and are found therein when the fermen-tation is finished mixed with the products of thedecomposition of the sugar. These general con-siderations must be borne in mind whilst pro-ceeding to the separation and estimation of theproducts of the fermentation.
The weight of the yeast employed must first becarefully determined, and an equal weight of thesame yeast must be dried at 212° Fahr. (100° C.),and then weighed, so that the amount of dry matterwhich the yeast contains may be known.
When, on attentively examining the fermentingliquid for some minutes, no bubbles of gas are seen torise, we may conclude that the fermentation is finished,unless the alcoholic is complicated with the lacticfermentation, in which case the disengagement ofgas may cease while a good deal of sugar remainsundecomposed. But this is an exceptional case,which only occurs when the yeast employed is staleand contains some of the lactic ferment. In ordinarycases, with a weak solution of sugar, the fermentationis finished in from fifteen days to three weeks, butwhen an exeess of sugar and but little yeast areemployed, it may last for months or even years.
The fermented liquor is now filtered through afilter tarod with another of the same paper. Afterdrying at 212° Fahr. (100° C.), one weighing will givethe weight in the dry state of the yeast deposited inthe course of the fermentation. The filtered liquidis then very slowly evaporated to a small bulk, andthe evaporation is finished in a vacuum. Aftertwenty-four hours the syrupy residue is treated sevenor eight times with a mixture of one pint of alcoholand one and a Half pints of ether. Each washing
Distillation.
should be filtered, although generally the insolublematter remains as a plastic mass at the bottom ofthe capsule. To determine the amount of thisinsoluble matter it is only necessary to redissolve itin water, evaporate it in a water bath in a weighedcapsule, and dry in a stove at 212° Fahr. (100° C.)until the weight is constant.
The flask containing the alcoholic ethereal solutionis placed in warm water to drive off the greater partof the ether; the evaporation is then continued at avery gentle heat, and finished as before in vacuo.Pure and perfectly clear lime-water is then added,to exactly neutralize the acid. The evaporation isrepeated with the same precautions, and the residueagain treated with the mixture of alcohol and ether,to dissolve the glycerine. The succinate of limeremains behind in a crystalline state, contaminatedwith a small quantity of extractive matter, or lime-salt of an uncrystallizable acid. These impurities maybe removed by digesting the succinate of lime fortwenty-four hours with alcohol, which dissolves theforeign matters, and leaves the succinate sufficientlypure. It may then be collected on a tared filter,dried and weighed.
The glycerine may be weighed after havingevaporated the alcoholic solution at a gentle heat,the evaporation being completed under the air-pump;where, however, it must not remain longer than twoor three days, as it continues to lose weight afterbeing deprived of water. In this way all die glycerineis obtained without loss, and it may be regarded aspure when the liquid has been fermented under theinfluence of a sufficient but not unnecessarily largequantity of yeast. When much more yeast than isnecessary has been used, the glycerine will have asharp bitter taste, because although the yeast itselfhas been removed by filtration, it contains a verysmall quantity of acrid matters which are soluble inthe mixture of alcohol and ether. Fermentation byitself gives nothing which can render the glycerineimpure when extracted as above.
One hundred grammes of sugar candy, fermentedwith 1T98 grammes of dry yeast, gave after the fer-mentation :—
Succinic acid. 0-673 grammes.
Glycerine,. 3-G40 “
Total,. 4-313 “
That the elements of the glycerine are furnished
by the sugar, and that the yeast contributes nothingto it, is proved by a comparison of the weights of theglycerine and yeast in the preceding experiment. Butin this case it is not so clear with regard to succinicacid. It is possible, however, by a particular ex-periment, to obtain an amount of succinic acid largerthan the soluble matter of the yeast employed.The succinic acid, therefore, is formed from thesugar as well as the glycerine, and the elements ofthe yeast take no part in the formation of theseproducts.
Distillation. —The chief object of importance inthis stage is the still; and no other article of manu-facturing apparatus has undergone so much alteration.