278 Mr. Faraday on Chemical Manipulation. 



practical information ; and the same remark applies to the 

 succeeding sections on comminution and solution — indeed, we 

 were surprised at finding so much to be taught in regard to 

 these very simple operations. The seventh, eighth, and 

 ninth sections treat of distillation and sublimation, precipita- 

 tion, and filtration. Here, and indeed throughout the work, 

 the wood-cuts are particularly distinct and well executed* 

 In the section on crystallization, the uses of that process are 

 enumerated ; and to this succeeds an account of evaporation. 

 All these operations are extremely well investigated and de- 

 scribed, both as to their principles and as to the most proper 

 meansof effecting them; a numlDer of curious circumstances 

 are pointed out, by which their results are influenced, and 

 by which certainty and success may be insured. 



The uses of coloured tests are explained and illustrated in 

 the twelfth section. Of coloured liquids the author chiefly 

 recommends the infusion of red cabbage ; and as it is not only 

 a very good test for private experiments but of excellent 

 service to the public lecturer in rendering certain changes of 

 composition visible to an audience, it may be worth while 

 extracting the directions for preparing it. 



" 583. The only substance of the kind, perhaps, worth 

 keeping in solution, is an acid infusion of red cabbage. For 

 its preparation, one or more red cabbages should be cut into 

 strips, and boiling water poured upon the pieces ; a little 

 dilute sulphuric acid is to be added, and the whole well 

 stirred: it is then to be covered and kept hot as long as 

 possible, or, if convenient, should be heated nearly to boiling, 

 for an hour or two, in a copper or earthen vessel. The 

 quantity of water to be added at first should be suflScient to 

 cover the cabbage, and the sulphuric acid should be in the 

 proportion of about half an ounce of strong oil of vitriol by 

 measure to each good-sized plant. This being done, the 

 fluid should be separated and drained off, and as much more 

 hot water poured on as will cover the solid residue, adding 

 a very little sulphuric acid. The whole is to be closed up, 

 and suffered to stand until cold, and then the liquid poured 

 ofi^ and added to the former infusion. The cabbage may 

 now be thrown away. The infusion is to be evaporated to 

 one half or one third its first bulk, poured into a jar, allowed 

 to settle, and the clear red fluid decanted and preserved in 

 bottles. The residue may have water added to it, the solid 

 part be allQvved to subside, the clear liquor drawn oft', eva- 

 porated and added to the former, or it may be dismissed 

 altogether* This solution will keep for a year. When re- 



