§ 189. =The detection and estimation of chloroform= from organic substances is not difficult, its low boiling-point causing it to distil readily. Accordingly (whatever may be the ultimate modifications, as suggested by different experimenters), the first step is to bring the substances, unless fluid, into a pulp with water, and submit this pulp to distillation by the heat of a water-bath. If the liquid operated upon possesses no particular odour, the chloroform may in this way be recognised in the distillate, which, if necessary, may be redistilled in the same manner, so as to concentrate the volatile matters in a small compass. There are four chief tests for the identification of chloroform:-- (1.) The final distillate is tested with a little aniline, and an alcoholic solution of soda or potash lye; either immediately, or upon gently warming the liquid, there is a peculiar and penetrating odour of phenylcarbylamine, C₆H₅NC; it is produced by the following reaction:-- CHCl₃ + 3KOH + C₆H₅NH₂ = C₆H₅NC + 3KCl + 3H₂O. Chloral, trichloracetic acid, bromoform and iodoform also give the same reaction; on the other hand, ethylidene chloride does not yield under these circumstances any carbylamine (isonitrile). (2.) Chloroform reduces Fehling’s alkaline copper solution, _when applied to a distillate_, thus excluding a host of more fixed bodies which have the same reaction; it is a very excellent test, and may be made quantitative. The reaction is as follows:-- CHCl₃ + 5KHO + 2CuO = Cu₂O + K₂CO₃ + 3KCl + 3H₂O; thus, every 100 parts of cuprous oxide equals 83·75 of chloroform. (3.) The fluid to be tested (which, if acid, should be neutralised), is distilled in a slow current of hydrogen, and the vapour conducted through a short bit of red-hot combustion-tube containing platinum gauze. Under these circumstances, the chloroform is decomposed and hydrochloric acid formed; hence, the issuing vapour has an acid reaction to test-paper, and if led into a solution of silver nitrate, gives the usual precipitate of argentic chloride. Every 100 parts of silver chloride equal 27·758 of chloroform. (4.) The fluid is mixed with a little thymol and potash; if chloroform be present, a reddish-violet colour is developed, becoming more distinct on the application of heat.[176] [176] S. Vidali in _Deutsch-Amerikan. Apoth.-Zeitung_, vol. iij., Aug. 15, 1882.