282 



are, like liquor of ammonia, never nsed for directly extracting the 

 plant, but only for separating mixed substances. In some cases 

 they have proved very viseful in sepai*ating a substance from tena- 

 ciously attached colouring particles, the latter being insoluble, or 

 nearly so, in those liquids, while, on the contrary, they prove 

 excellent solvents for alkaloids, resins, &c. The solvent may be 

 finally removed, either by evapoi'ating (chloroform, wood-spirit, 

 sulphide of carbon); or the alkaloids are withdrawn from their 

 respective solutions in benzol, petroleum, or oil of turpentine by 

 shaking with water acidulated with hydrochloric acid, as evapora- 

 tion at a high temperature would be impracticable. 



C. — Reagents. 



A. — Examination of the dry substance. 



The first trial consists in exposing the respective substance 

 to the action of heat, when is to be observed whether fusion, 

 either total or partial volatilisation, or carbonisation takes place. 



In the first case, i.e., with a fusible substance, is to be 

 determined the fusing-jwint, by inserting small pieces of about 

 the size of a millet-seed into a capillary tube, or with fats 

 or waxy matters by allowing them in the melted state to rise 

 into such a tube, and to congeal therein; then put this tube, 

 together with a thermometer reaching at least to 300°, into 

 a test-tube, the latter into a glass-flask, this on an iron plate, 

 and heat the latter by means of a spirit-lamp. The heating has 

 to be conducted very slowly and gradually, so as to enable a 

 careful observation of the mercury rising from degree to degree. 

 The height of the mercury is read ofi" and noted down as soon as 

 the fat begins to melt, without being entirely fluid. The latter 

 precaution is necessary, becaiise in the transition from the solid 

 into the liquid state heat is absorbed and becomes latent, causing 

 either a stoppage of the mercury, or" even a retrogi'essive move- 

 ment. — Eveiy estimation of the fusing-point has to be made 

 at least twice, and if the two experiments do not harmonise, 

 oftener. 



After complete fusion and with increased heating, the substance 

 sublimates, if volatile ; if not, decomposition takes place, indicated 

 by the black colour assumed by the substance, and by the 

 emission of empyreumatic gases. Yet, it sometimes happens, 

 T/hat substances sublimate or decompose without havmg been 

 fused first. In a capillaiy tube this cannot be observed satis- 

 factorily, because the liquid sample in it rises mechanically under 

 the influence of the heat without having been sublimated at all, 

 and because the tube is too narrow for inserting slips of test- 

 paper. — Repeat, therefore, the experiment with a fresh sample, 



