280* Mr. Faraday on Chemical Manipulation, 



paper tlius modified is used to detect a free alkali, instead 

 of turmeric paper, that substance is indicated by the restora- 

 tion of the original blue colour. Litmus paper is best 

 slightly reddened for this use, by putting a drop or two of 

 muriatic acid into a large jar, allowing it to stand a few 

 minutes, and then bringing the paper towards the mouth of 

 the jar, or carefully placing it within : so soon as the blue 

 tint has become slightly reddened, the paper should be re- 

 moved for use. If too much acid be imparted to the paper, 

 the delicacy of its indications is injured, because of the 

 greater quantity of alkali required to neutralize the acid, 

 and restore the blue colour. For the same reason a paper 

 free from alkali or carbonate of lime has been recommended 

 for the preparation of these tests : for these impurities, 

 combining with a minute portion of acid, neutralize it, and 

 thus prevent that delicacy of indication which the test paper 

 ought and may be made to possess." 



The mode of determining the value of alcaline substances, 

 or " alcalimetry," is described at length in this section. Our 

 readers, however, will here recollect that there is an error 

 respecting thespecificgravity of the acid, which Mr. Faraday 

 has corrected at page 221 of the present volume of this Jour- 

 nal. The thirteenth section is allotted to crucible operations, 

 and the fourteenth to furnace tube operations. They are 

 full of minute and admirable instructions, evidently deduced 

 from long experience, and detailed with the same precision 

 and clearness which we have already eulogised. The fifteenth 

 section, which occupies nearly a hundred pages, relates to 

 " pneumatic manipulation, or management of gases." Every 

 paragraph of the instructions here given will be found to 

 contain something of importance to the student ; it is, indeed, 

 a valuable essay upon a difficult and nice department of 

 chemical research. --}■,■ *"' i// irjv.-v. 



Under the head " Tube Chemistrf;^ in the sixfeeftth sec- 

 tion, a variety of means are pointed out, of working with and 

 employing glass-tubes, as substitutes for more expensive and 

 formal apparatus. Indeed, the young chemist cannot do 

 better than practise the art of bending, drawing out, and 

 sealing tubes, as here directed, (and in the nineteenth section,) 

 by which he will soon gain the requisite dexterity in forming 

 them into test tubes, retorts, and so on, and be enabled to 

 furnish his laboratory with a quantity of very useful vessels 

 and apparatus, at a very moderate expense. 



The application of electricity to chemical purposes forms 

 the subject of the seventeenth section, in which the manage- 



