2S 



NA TURE 



[November i i, 1897 



ORGANIC CHEMICAL MANIPULATION. 

 Organic Chemical Manipulation. By J. T. Hewitt, M.A., 

 D.Sc. Pp. xi + 253. (London : Whittaker and Co., 

 1897.) 



THIS is in some respects a useful little book, but it 

 might easily have been made much more useful. 

 It is divided into two parts. The first portion — 102 pages 

 — is occupied mainly with a very brief description of 

 processes of purifying organic substances, namely, crystal- 

 lisation, distillation, melting-point determination, and sub- 

 limation ; and a short outline of the processes of ultimate 

 organic analysis. A large part of the matter in this section 

 of the book is what the student will find in almost any 

 text-book on quantitative analysis, and might perhaps 

 with advantage have been omitted here, and its space 

 devoted to an extension of the matter in Part ii., and to 

 more exact and detailed directions for carrying out the 

 "manipulations" therein described. The second part of 

 the book, covering 1 50 pages, is on the " preparation of 

 organic substances." This, at least, is what it professes 

 to be; but there is so much "descriptive" matter dis- 

 tributed throughout it, that in parts it more resembles a 

 simple text-book on organic chemistry, with experiments 

 thrown in. For example, after giving very fair directions 

 for the preparation of methane from sodium acetate, and 

 the performance of two or three experiments illustrative 

 of its properties, the author proceeds to describe, in the 

 true text-book style, the various other methods for the 

 preparation of marsh gas. Thus : — ' 



" To obtain perfectly pure methane, zinc-methyl is 

 decomposed by water : 



Zn(CHa)2 + 2H,0 = 2CH4 + ZnlOH),. 



An interesting synthetical method for the formation 

 of methane was discovered by Berthelot, who led a mixture 

 of sulphuretted hydrogen and the vapour of carbon di- 

 sulphide over red-hot copper : 



CS2 + 2H.S + 8Cu = CH4 -(- 4CU2S. 



The following general methods of the formation 

 of paraffins, i.e. hydrocarbons of the general formula 

 CuH2n + 2, may be mentioned." 



And so on, and so on (pages 106-7). 

 Again, we read : 



" The aldehydes are nearly always produced by the 

 oxidation of the corresponding primary alcohols, the pro- 

 cess being usually carried out with potassium dichromate 

 and sulphuric acid, e.g. : 



3CH3CH2OH + KaCrjO, -|- 4H..SO4 = 3CH3 . CHO + K.iS04 

 + CT,(SOi)s + 7H,0. 



Another way is to distil a mixture of the barium or 

 calcium salt of an acid with the corresponding formate ; 

 the following reaction then takes place : " 



And so on for nearly three pages. This is all very 

 true, and good enough of its kind ; but it savours too 

 much of the ordinary descriptive text-book, and too little 

 of " Organic Chemical Manipulation." 



Why such " manipulations " as taking the density or 



specific gravity of an organic liquid, or finding the 



optical activity of a sugar solution, should be introduced 



in the part of the book supposed to be devoted to the 



NO. 1463, VOL. ^y] 



"preparation of organic substances" is not quite 

 evident. The directions given for the preparation of the 

 various compounds dealt with, although often very good, 

 are not always above criticism ; for example, in the pre- 

 paration of ethylene the student is directed to mix 25 

 grams of alcohol and 1 50 grams of strong sulphuric acid 

 in a flask of two or three litres capacity. Why such an 

 enormous flask ? The total volume of the mixture is 

 barely 100 c.c, with at most another 50 c.c. to be added 

 as the operation goes on, and to employ a flask of 20 or 

 30 times this capacity is simply ridiculous. Without 

 adopting any of the well-known precautions against 

 frothing up (which, by the way, are not hinted at), if the 

 flask is not more than one-fourth filled with the liquid it 

 will be amply large enough. The author then goes on 

 to direct that the gas shall be passed through two wash- 

 bottles in succession, 



"the first being charged with concentrated sulphuric 

 acid to remove the vapours of alcohol and ether, the 

 second with caustic soda solution to hold back any 

 carbon dioxide, and towards the end of the experiment 

 sulphur dioxide." 



As water, in the form of steam, is expelled from the 

 generating flask in considerable quantity along with the 

 ethylene, the strong sulphuric acid in the first wash- 

 bottle will soon become weak sulphuric acid, and more- 

 over will become so hot as to render the fracture of 

 the bottle extremely probable. If these two wash-bottles 

 are to be used, the order should be reversed ; but as a 

 matter of fact they are quite unnecessary. If the 

 temperature is properly regulated (for which purpose a 

 thermometer should be passed through the cork of the 

 generating flask, and should dip into the liquid), prac- 

 tically no ether is produced ; and if the gas is passed 

 through a single wash-bottle containing water, any 

 alcohol which passes over will, for the most part, be 

 retained there. So also^will any sulphur dioxide, should 

 the operation be pushed to such extremes that this gas 

 is generated. Any traces of carbon dioxide which ac- 

 company the ethylene are quite immaterial, but they can 

 if necessary be absorbed by the addition of a little caustic 

 soda to the water in the pneumatic trough. 



Lastly, after directing that the gas is to be passed 

 through two bottles containing bromine, for the prepara- 

 tion of ethylene dibromide, the author adds, " the tube 

 leading from the bromine absorption bottles must not 

 open directly into the air, but should go into the bottom 

 of a lime-tower which is charged from the constriction 

 upwards with alternate layers of broken glass and soda- 

 lime." Why not simply bubble the gas through a little 

 caustic soda in a small beaker ? 



On p. 112 the following equation is given for the 

 preparation of cuprous acetylide : — 



C.,H., + CuCI + NH3 = C,HCu + NH4CI. 



One would like to know upon whose authority this is 

 given. 



The book contains sixty-three illustrations, most of 

 which are of the very roughest description. Fig. 36, p. 

 67, represents a crucible balanced in an impossible 

 position upon a pipe-clay triangle. Again, in Fig. 60, p. 

 183, it is difficult to see why an exit tube is to be 



