In order to identify the substance, the ether extract, after neutralisation, is allowed to evaporate to a syrup, and crystallisation promoted either by rubbing with a glass rod, or by the more certain and highly characteristic method of 'sowing' with the most minute trace of ω-brommethylfurfural, when crystals are almost instantly formed. These are recrystallised from ether, or a mixture of ether and light petroleum, and further identified by the melting-point (59.5-60.5°), and, if considered desirable, by estimation of the bromine.
It is now found, so reactive is the bromine atom in this compound, that the estimation may be accurately made by titration with silver nitrate according to Volhard's process, the crystals for this purpose being dissolved in dilute alcohol:
0.1970 gram required 10.5 c.c. N/10 AgNO3. Br = 42.63 p.ct., calculated 42.32 p.ct.
This method of applying hydrogen bromide in ethereal solution is, of course, unsuitable for investigations where a higher temperature has to be employed, or where long standing is necessary, since, under such circumstances, the ether itself is attacked. Wishing to make investigations under these conditions, the authors have tried several solvents, and, at present, find that chloroform is best suited to the purpose. In each of the following experiments, 10 grms. of the substance were covered with 250 c.c. of chloroform which had been saturated at 0° with dry hydrogen bromide. The mixture was contained in an accurately stoppered bottle, firmly secured with an iron clamp, and heated in a water-bath to about the boiling temperature for two hours. After standing for several hours, the mixture was treated with sodium carbonate (first anhydrous solid, and afterwards a few drops of strong solution), filtered, and the solution dried over calcium chloride. Most of the chloroform was then distilled off, and the remaining solution allowed to evaporate to a thick syrup in a weighed dish.
The product was then tested for ω-brommethylfurfural by 'sowing' with the most minute trace of the substance, as described above. It was then warmed on a water-oven, kept in a vacuum desiccator over solid paraffin, and the weight estimated. When necessary, the product was recrystallised from ether, and further identified by the tests mentioned. The following results were obtained:
| Weight of crude residue. | |||
| Swedish filter paper | 3.0 | crystallised at once | by 'sowing.' |
| Ordinary cotton | 3.3 | " | " |
| Mercerised cotton | 2.1 | " | " |
| Straw cellulose[6] | 2.3 | " | " |
| Lævulose | 2.2 | " | " |
| Inulin | 1.3 | " | " |
| Potato starch | 0.37 | " | " |
| Cane sugar | 0.85 | " | " |
| Dextrose | 0.33 | uncrystallisable. | |
| Milk sugar | 0.37 | " | |
| Glycogen | 0.34 | " | |
| Galactose | 0.34 | " | |
The products from dextrose, milk sugar, and galactose absolutely refused to crystallise even when extracted with ether and again evaporated, or by 'sowing,' stirring, &c.
The glycogen product deposited a very small amount of crystalline matter on standing, but the quantity was too minute for examination; moreover, it refused altogether to crystallise in contact with the aldehyde. It may fairly be stated, therefore, that these last four substances give absolutely negative results as regards the formation of ω-brommethylfurfural; if any is formed, its quantity is altogether too small to be detected.
The specimen of starch examined was freshly prepared from potato, and purified by digestion for twenty-four hours each with N/10 KOH, N/4 HCl, and strong alcohol; it was then washed with water and allowed to dry in the air. It will be seen that this substance gave a positive result, but that the yield was extremely small, and might yet be due to impurity. Considering the importance of the behaviour of starch, for the purpose of drawing general conclusions from these observations, it was thought advisable to make further experiments with specimens which could be relied upon, and also to investigate the behaviour of dextrin. This the authors have been enabled to do upon a series of specimens specially prepared by C. O'Sullivan, and thus described by him: