(2.) Glycerin obtained by calcareous saponification, also may contain oleate of lime. This may be detected with oxalate of ammonia, which throws down the lime as a clearly perceptible precipitate.
The colour of glycerin is in no way an index of the purity of the product. In all cases it is useful to be assured of the neutrality of the glycerin.
The preceding tests are suited for glycerins more or less impure, but not adulterated. According to the authors’ experiments the tribasic acetate of lead separates all the foreign substances due to normal impurity of the product or alteration in the glycerin during its manufacture. Any addition of glucose may be detected by Fehlings’ solution.
Quantitative Test. This test should comprehend the determination of the water, the foreign organic matter, the lime, and the glycerin.
In the following table the authors have given the density of various mixtures of water and glycerin, comparatively with the degrees Baumé, and also the proportions of water corresponding to the densities. They state, that these determinations have been verified by means of pure anhydrous glycerin, prepared by keeping glycerin for several hours at a temperature of 160° C, and terminating the operation in vacuô. The density found was in accord with that given by Berthelot, namely, 1·264.
Estimation of Organic Matter. Fifty grams of glycerin diluted with water are treated with an excess of tribasic acetate of lead, and the precipitate collected on two tared filters, and the lead compound weighed. The whole is then calcined, the residue treated with nitric acid, and then with sulphuric acid, and from the sulphate of lead is calculated the quantity of oxide of lead, that was in combination with organic matters, and consequently the proportion of the latter, which rarely exceeds 1 to 1·5 per cent.
Lime may be estimated in the usual manner by oxalate of ammonia.
| Hydrometer Weight of Litre. | Areometer Degrees, Baumé. | Water, per Cent. |
| 1264·0 | 31·2 | 0·0 |
| 1262·5 | 31·0 | 0·5 |
| 1261·2 | 30·9 | 1·0 |
| 1260·0 | 30·8 | 1·5 |
| 1258·5 | 30·7 | 2·0 |
| 1257·2 | 30·6 | 2·5 |
| 1256·0 | 30·4 | 3·0 |
| 1254·5 | 30·3 | 3·5 |
| 1253·2 | 30·2 | 4·0 |
| 1252·0 | 30·1 | 4·5 |
| 1250·5 | 30·0 | 5·0 |
| 1249·0 | 29·9 | 5·5 |
| 1248·0 | 29·8 | 6·0 |
| 1246·5 | 29·7 | 6·5 |
| 1245·5 | 29·6 | 7·0 |
| 1244·0 | 29·5 | 7·5 |
| 1242·7 | 29·3 | 8·0 |
| 1241·2 | 29·2 | 8·5 |
| 1240·0 | 29·0 | 9·0 |
| 1239·0 | 28·9 | 9·5 |
| 1237·5 | 28·8 | 10·0 |
| 1236·2 | 28·7 | 10·5 |
| 1235·0 | 28·6 | 11·0 |
| 1233·5 | 28·4 | 11·5 |
| 1232·2 | 28·3 | 12·0 |
| 1230·7 | 28·2 | 12·5 |
| 1229·5 | 28·0 | 13·0 |
| 1228·0 | 27·8 | 13·5 |
| 1227·0 | 27·7 | 14·0 |
| 1225·5 | 27·6 | 14·5 |
| 1224·2 | 27·4 | 15·0 |
| 1223·0 | 27·3 | 15·5 |
| 1221·7 | 27·2 | 16·0 |
| 1220·2 | 27·0 | 16·5 |
| 1219·0 | 26·9 | 17·0 |
| 1217·7 | 26·8 | 17·5 |
| 1216·5 | 26·7 | 18·0 |
| 1215·0 | 26·5 | 18·5 |
| 1213·7 | 26·4 | 19·0 |
| 1212·5 | 26·3 | 19·5 |
| 1211·2 | 26·2 | 20·0 |
| 1210·0 | 26·0 | 20·5 |
| 1208·5 | 25·9 | 21·9 |
The authors consider that industrially the
tribasic acetate of lead might be used for the removal of organic matter from crude glycerin.