GLYCERINE (Formula H, (OH), ; molecular weight, 92 ; synonyms glycerin, glycerol, pro. phenyl alcohol). Discovered by Scheele in 1779. It is a colorless, viscid, neutral, inodorous fluic having a very sweet taste. It is soluble in water and alcohol in all proportions, but insoluble ir ether and in chloroform. It should possess a specific gravity of above 1•23. If below this, it is in all probability diluted with water. To ascertain the quantity of water present the following formula is generally used :— x 000d 2.66d Here d is the specific gravity of the sample tested as compared with water, at a temperature of 6o° F, and P the percentage of glycerine actually present, provided also that it contains no other matters.
Glycerine occurs ready formed in a few fats, and is always produced in the alcoholic fermen tation of sugar ; hence it occurs in all fermented liquors.
The usual method of its production for commercial purposes is by distilling fats in a cur rent of superheated steam at 300°, when the fats are decomposed, and the glycerine which distil: over is finally rectified in vacuo.
A simple method of obtaining it on a small scale is from olive oil, which is saponified by treating it with an equal weight of lead oxide. This is mixed with water and added to the oil with which it is boiled till the saponification is complete. The glycerine is dissolved by the water and is easily separated from the insoluble lead plaster. Any traces of lead are removed by sul. phuretted hydrogen, and the water is expelled in vacuo, as the glycerine would turn brown it the air.
The adulterations used in the manufacture of glycerine are glucose and cane sugar. Other matters are often present, such as lead calcium, and formic and oxalic acid, their presence being due to imperfect purification. To detect the presence of glucose, boil a small portion of the sam•
ple with an excess of caustic soda and a few drops of copper sulphate. If any be present a me precipitate will be the result. To test for cane sugar boil for half an hour with sulphuric acid. This will convert any cane sugar into glucose, when it can then be tested as described above Lead and calcium are detected by burning the glycerine, and dissolving the residue in a few drops of nitric acid. The solution thus obtained is then diluted with water and divided into twc quantities. Pass sulphuretted hydrogen through one and a black precipitate will show the pres.
ence of lead, and add a small quantity of ammonium oxalate to the other portion, and a white precipitate proves calcium to be present. Oxalic acid is detected by the white precipitate it yields with calcium acetate and formic acid by blackening on warming a diluted sample with ammonio nitrate of silver.
Glycerine is an antiseptic, and is used in photography principally for this reason. It is used as a preservative of gyro solutions, and is added to gelatine emulsions to prevent decomposition. A small quantity added to water will prevent it freezing, except at a low temperature. It is also used as restraining agent in developing, but its action in this case is purely physical.
Glycerine is extremely hygroscopic, and cannot be dried by heat without decomposition. Its non-drying property causes it to he used for many purposes to prevent too rapid drying of substances. A small quantity is added to gelatine emulsion spread upon paper, which causes the film to become more pliable and less easily cracked. Glycerine burns with a colorless flame, and dissolves iodine.