The receiver is changed, and the "heavy oil" comes over; towards the end a thick brown or yellow viscid product is got. The receiver is again changed, and the distillation carried to dryness.
The "crude light oil" is washed cold with 2 per cent. of sulphuric acid (concentrated), and afterwards with excess of soda. Thus purified it is again distilled to dryness, three fractions being collected as before. Naphtha, which is added to the main portion, and measured; "light oil," which is also measured; and "heavy oil," which is added to that got in the first distillation. This last is poured into a flat-bottom capsule, and allowed to cool slowly. The temperature may with advantage be carried below freezing-point. The cooled cake is pressed between folds of linen, and the paraffin scale detached and weighed.
The results may be reported thus:—
| Naphtha, sp. g. | —— |
| Light oil, sp. g. | —— |
| Heavy oil, sp. g. | —— |
| Paraffin scale | —— |
| Coke, &c. | —— |
The results are calculated in per cents. on the oil taken. Some workers take their fractions at each rise of 50° C. The composition of average shale, as given by Mills, is as follows:—Specific gravity, 1.877; moisture, 2.54.
| Gas | } | |
| Volatile matter, water, ammonia | } | 23.53 |
| Oil | } | |
| Fixed carbon | 12.69 | |
| Ash | 63.74 | |
| _____ | ||
| 99.96 |
The ash is made up of silica, 55.6; ferric oxide, 12.2; alumina, 22.14; lime, 1.5; sulphur, 0.9; soluble salts (containing 0.92 per cent. sulphuric oxide), 8.3.
| Total | sulphur | in shale | 1.8 | per cent. |
| " | " | in ash | 1.3 | " |
For further information on these assays, and for the assay of petroleums, bitumens, &c., the student is referred to Allen's "Commercial Organic Analysis," Vol. II.
Determination of Organic Carbon in a Limestone.—Take 1 or 2 grams and dissolve with a very slight excess of dilute hydrochloric acid, evaporate to dryness, and determine the carbon in the residue by combustion with copper oxide.