180 Chemical Aids to Art. 



instead of silvered flats,, no fault will be found with the colour 

 of the objects viewed. A slightly tarnished flat, exaggerating 

 the peculiar chromatic action of the silver film, gives an 

 unpleasant reddening to white objects ; a fine prism is quite 

 satisfactory, but it must really be a fine one, for very slight 

 errors in its planes, and especially in the plane of the hypo- 

 theneuse, will render good definition impossible. 



Mr. Browning's pamphlet, A Plea for Reflectors, contains 

 a mass of valuable information, which we commend to those 

 in need of it. 



CHEMICAL AIDS TO ART. 



BY PROFESSOR A. H. CHURCH, M.A., F.C.S., 

 Of the Royal Agricultural College, Cirencester. 



Some of the recent applications of chemistry to the fine arts 

 are so full of interest, and yet so little known in scientific and 

 literary circles, that a brief description and explanation of them 

 is sure to prove instructive and entertaining to many of the 

 readers of the Intellectual Observer. The subject is, 

 indeed, very extensive, and on this account we propose, in the 

 present paper, to limit the discussion to a few processes con- 

 nected with the ornamental and artistic use of metals. We 

 shall select three processes, all comparatively of recent inven- 

 tion ; of none of them, so far as we are aware, has any 

 account been hitherto published. They, moreover, have the 

 advantage of being easily illustrated in home-made experi- 

 ments, by any of our readers who care to follow the instruc- 

 tions about to be given. 



Let us begin with platinum, one of the least known of the 

 " precious" metals. Precious it is for several reasons. Not 

 that it is very beautiful in colour and lustre, for although it 

 may be obtained nearly as white as silver, its appearance 

 usually resembles that of pewter very closely ; yet time and 

 experiment have shown that it has most valuable properties. 

 It never tarnishes, no ordinary flame, or fire, or furnace will 

 melt it, most strong acids and many chemical salts do not 

 dissolve or injure it ; and, when you do get it to dissolve, its 

 solution forms a most useful chemical test, or "reagent/' as 

 it is called. Since the year 1741, when platinum was first 

 brought to Europe, under the name of platina, or " little 

 silver," it has been employed for many different purposes. 

 As it could not be worked like ordinary metals, the Kussiaus, 



