til 



OLCTIN. 



GLYCERIN. 



HI 



OLUTIN. 



OLYCKKAMlNa 



GLYCKKK .U ID (C.H.O.). This body was first discovered by 

 Debus, who obtained it by the oxidation of glycerin by mean* uf nitric 

 acid. One |rt uf glycerin mixed with iU volume of water is placed in 

 an upright cylinder, and one part of itrong nitric acid allowed to flow 

 underneath the glycerin. The two layer* gradually mix, and oxidation 

 takes place with disengagement of gas. After the action it over, the 

 product i> evaporated in amall quantities in the water bath, diluted 

 with water, neutraliaed with chalk, and strong alcohol added, which 

 precipitatea the lime salt*. Then are then diiaolved in warm water, 

 filtered, and to the filtrate excess of milk of lime U added, which 

 precipitate* certain impurities. The liquid U again filtered, the free 

 lime removed by carbonic acid, and the liquid evaporated to cry 

 talliiatiiMi 



The acid U obtained by precipitating the lime-salt with, oxalic avid, 

 and evaporating the filtrate m the water bath. In iU state of greatest 

 concentration it U a thick yellowish syrup, which dried at 281 Fahr. 

 has the appearance of gum arable. It readily attracts uiuutiin . 1 1 - 

 aqueous solution decomposes carbonates, coagulates milk, and dissolves 

 iron and cine with disengagement of gas. The salts of glyceric acid 

 crystallise well ; they have the genera] formula C,H S MO,. 



Glyceric acid can be considered as being derived from glycerin in 

 the same manner as glycolic acid from glycol, or as acetic acid is 

 derived from ordinary alcohol : 



Alcohol. 



Glycol. 



Acetic acid. 



cc.H,o,rj 0< 



Glycolic acid. 



Gljrwriu. 



Glyceric acid. 



According to this view of its constitution, glyceric acid is tribasic, 

 But the salts of glyceric acid, as far as they have been examined, are 

 monobasic. In order to decide the question as to the basiscity of 

 elvceric acid, the ethers and the amides ought to be investigated : until 



(C H O '"> ) 

 this is done, the formula may be written v ' |, - } O, although it 



must be confessed that at present this view U nothing more than a 

 probable hypothesis. 



QLTCKEUDES. [GLYCERIN.] 



GLYCERIN (C.H.O.), Mydrattd oxide of lipyt. This substance 

 was discovered by Scheele in 177!*, who obtained it in the pre| 

 of lead plaster. He named it, " sweet principle of oils," from its sweet 

 taste. Subsequently, its properties were more accurately studied by 

 Chevreul in his classical investigations on the chemical history of 

 bodies of fatty origin, and by Pelouze. Recently Berthelot and De 

 Luca have greatly extended our knowledge of this substance. 



Host of the fats and oils of the animal and vegetable kingdoms 

 have a constitution analogous to that of the compound ethers, -acetic 

 ether, for example. When that substance is treated with alkalies it 

 assimilates the elements of'water, forming an alkaline acetate and 

 alcohol. Oils and fata in like manner undergo by the same treatment 

 a similar change. They assimilate the elements of water, glycerin is 

 set tree, and a salt of the acid, previously in combination with glycerin, 

 U formed. On this decomposition the methods of preparing glycerin 

 are based. 



Glycerin may be prepared by saponifying oils with oxide of lead : 

 equal parts of olive oil and of finely powdered litharge are mixed in a 

 basin with water, the mixture heated to boiling for gome time, and 

 continually stirred, water being added to replace that which evaporates. 

 Insoluble lead salts (in this case, the oleate and stearate of lead) are 

 formed ; warm water is then added, and the aqueous liquid decanted, 

 filtered, and sulphuretted hydrogen rinnnii through the filtrate, in 

 order to precipitate a small quantity of oxide of lead, which dissolves. 

 The filtered liquid is then evaporated in vacuo, or over Ui> 



Glycerin u also obtained as a by-product in the manufacture of 

 stearin candles, in which case, the saponification is effected by means 

 of lime. 



But the simplest method, and that to which we owe the abundant 

 and cheap supply of glycerin met with in commerce, is the one 

 introduced by Wilson. It consists in treating the fats in a - 

 distilling apparatus with superheated steam. The fats assimilate the 

 elements of water, and are decomposed into their constituents- -the 

 fatty acids and glycerin. Both distil over, and form in the recipient 

 two layers of liquid, of which the lower U tolerably pure aqueous 

 glycerin. To purify it still further it may be again distilled with high 

 pressure steam, concentrated in the water bath, and ultimately in 

 ncuo over sulphuric acid. 



Pure glycerin U a colourless, viscous, neutral, inodorous li<|iii<l, 

 with a sweet taste, from whence it derives its name (y\v*6i, sweet). 

 It is uncrystelliamble ; at 40 Fahr. it becomes gummy, and almost 

 olid. It is mutable with water and alcohol in all proportions, but is 

 insoluble in ether. It attracts moisture from the air, and ' 



more limpid. Concentrated M far a* possible in vacuo over sulphuric 

 .ici.l, it has the sp. r. 1-385 at 159* Fahr. It is difficultly . 

 only Ixxiii" ' ' di-til unchanged at 618 Fahr. When its aqueous 

 distilled Home glycerin passes off with the vapour. 



Pasteur has found that glycerin U contained in all fermented liquors, 

 and more especially in wine. Its quantity amounts to 3 per < 

 the fermented sugar. 



L)tcomptmtio of glyctri*. When glycerin U rapidly heated in a 

 closed vessel above iU boiling point, it is decomposed, with formation 

 of inflammable gues, acetic acid, and acrolein. Derivatives of gly- 

 cerin also, such as the natural oils and fats, by destructive distillation, 

 yield acrolein, the characteristic odour of which readily indicates the 

 presence of glycerin in any of these bodies. 



Mixed with platinum black, and placed in oxygen, glycerin absorbs a 

 huge quantity of this gas, with the formation of inadequately investi- 

 gated acid products, probably containing glyceric acid, which are 

 ultimately oxidised to carbonic acid and water. 



When an aqueous solution of glycerin is exposed in contact with 

 yeast to a temperature of 68-85" Fahr. for several months, a Urge 

 quantity of propionic acid is produced, together with some formic and 

 acetic acids. 



According to Berthelot, glycerin passes by fermentation into al 

 when it is left for some time in contact with chalk and decaying 

 cheese to a temperature of 85-1 05 Fahr. 



When glycerin is gently heated with hydrate of potash or soda, it is 

 converted into acetate and formiate, with liberation of hydrogen, 

 lein appears to be first formed, this then passes into acrylic acid, 

 which in turn is resolved into acetic and formic acids. 



In contact with aulndruus phosphoric acid, glycerin becomes 

 strongly heated, and acrolein is disengaged; this is also the case 

 when it is distilled with bisulphate of potash. 



Strong nitric acid converts glycerin in a great men 

 of id, C,H,0,. By a mixture of strong nitric and sulphuric acid- 

 converted into nitro-ylycerin C ( H > O t ,8N0 1 . 



The oily nature of glycerin, its property of not solidi 

 when exposed to great cold, its permanency, its pleasant taste, its 

 solvent powers, and the cheap rate at which it can be procured, will 

 eventually secure for it an extensive use in pharmacy, arts, and manu- 

 factures. A few of its applications may be here mentioned. 



It has been used to preserve articles of food, botanical and zoological 

 preparations. When added to confectionary wares, preserved 

 and chocolate, it serves to pi.\ ...t tin in from becoming dry. It 

 serves a similar purpose in the manufacture of tobacco and snuff. The 

 water in gas-meters is liable to freeze in winter, and evapor. 

 rapidly in summer : the addition of glycerin prevents these evils. 

 Glycerin U also used in the manufacture of copying ink, and in 

 lubricating. It is also used, under a patent, in preparing pa; 

 dry printing. 



iili/ceriilii, anil roiwtitutioii of glycerin. The glycerides are the com- 

 pound ethers of glycerin. To understand their nature the con.-titu 

 tion of glycerin must be understood, and the two points can best be 

 discussed together. 



The natural fats and oils, as previously stated, have a constitution 

 analogous to that of the compound ethers. This view of th. . 



i was first propounded by Chevreul. Afterwards, Duffy, in an 

 investigation of stearin, found that the quantity of stearine, which in 

 saponifying forms one equivalent of stearic acid, only forms one-third 

 of an equivalent of glycerin. Subsequently, Burthelot succeeded in 

 artificially forming a large quantity of the natural fats, by d 

 combining the acids with glycerin, and it is on these researches, and 

 on an interpretation ..t them proposed by Wurte, that the prevailing 

 views of their constitution are based. Berthelot found that the acids 

 could be made to combine with glycerin in three different proportion-, 

 with elimination of the elements of water, and he characterised glycerin 

 as a polyacid alcohol ; that is, as an alcohol in which several equiva- 

 lents of hydrogen are replaceable by acid radicals to form ether*. ll< 

 considered glycerin as bearing to alcohol a somewhat similar i 

 to that which tribasic phosphoric acid bears to nitric acid. 



Ordinary alcohol we may consider to be derived from the type of a 



double atom of water ' 



the substitution of the monoatomic 



radical ethyl for an atom of hydrogen ; and a compound ether is 

 alcohol, in which another atom of ,hydrogeu is replaced by an acid 

 radical, such as acctyl. Thus : 



In like manner we may consider glycerin to be derived from the 

 type of I/tree double atoms of water by the substitution of the teratomio 

 radical C, H.'" for three atoms of hydrogen. Thus : 



II 



i 



3 atom* of wnttr. 



