522 [April 16, 



iodine (dissolved in alcohol), carbonate of iron on which sulphuric 

 acid was poured, carbonate of iron on which glacial acetic acid was 

 poured, limestone on which sulphuric acid was poured, limestone on 

 which glacial acetic acid was poured, matches lighted under the 

 bell-glasses. The following did not colour the tests : Sulphuric 

 acid, glacial acetic acid, carbonate of lime, carbonate of iron, am- 

 monia, matches not lighted. 



The substances used in the manufacture of ordinary starch of com- 

 merce gave the following : 



Chloride of lime coloured the tests instantaneously. 



Sulphuric acid did not colour the tests. 



Lime did not colour the tests. 



Lime and sulphuric acid mixed coloured the tests rapidly. 



There are advantages in the powders over the ordinary tests. They 

 are more sensitive, and therefore more rapidly acted upon ; they re- 

 tain their maximum colour, not afterwards fading, as with the tests 

 of Schonbein and Moffat. (However, my calico and porous-paper 

 tests are not nearly so liable to fade, owing to the solution penetra- 

 ting into the fabric used, instead of being merely a surface-covering.) 

 There is also a more important advantage still to be mentioned from 

 the use of powders. By the aid of powder tests we shall ascertain 

 what colours the tests ; in the experiments it was found that a dif- 

 ferent colour was imparted to the powder, and that the colour pene- 

 trated deeper with some substances and acids than with others, so 

 that differences of effect took place, from which the different mate- 

 rials used might be recognized. Thus : 



1 . Iodine, although coloured a brown-black, was merely a surface 

 colouring, below the powder remained colourless. 



2. Phosphorus, bluish black on the surface only, below almost 

 colourless. 



3. Chloride of lime, deep brown on the surface only, the powder 

 below slightly yellow. 



4. Hydrochloric acid, grey-pink on the surface only, the powder 

 beneath orange. 



5. Nitric acid, dark-red brown extending slightly into the powder, 

 beneath that colourless. 



6. Carbonate of iron with glacial acetic acid, yellowish brown to 

 the thickness of cardboard, below that buff. 



