74 Difficulties encountered in manufacturing processes, 



processes and stages of processes through which 

 these substances have to pass, and to all the forces, 

 tools, machinery, and appliances employed in those 

 processes ; in the manufacture of glass, for example,, 

 the greatest care has to be exercised in the making 

 and gradual heating of the pots in which the glass 

 is melted, the proportions of the materials, the con- 

 struction of the furnaces, the management of the heat, 

 and a whole host of minor conditions too numerous 

 to mention, all of which must be attended to with 

 the greatest care. In the manufacture of iron and 

 steel, the smelting of copper, the refining of nickel,, 

 the preparation and baking of porcelain, and in 

 many other trades, innumerable difficulties, all having 

 their origin in the properties of matter and forces, 

 continually beset the manufacturers. In some cases 

 difficulties occur which perplex both the workman and 

 the scientific man called in to his aid, and so far 

 from an unscientific workman being able to overcome 

 them, even with the aid of the scientific man, he is 

 unable to do so. 



The hidden difficulties which beset a manufacturer 

 are not unfrequently so inscrutable that the present 

 state of knowledge in science fails to explain them. 

 Who can tell why it is that wire-work of brass or 

 German silver becomes gradually brittle by lapse of 

 time ? Or why varnish made in the open country has 

 different properties from that made in a town ? Or why 

 silk dyed in Lyons should possess a finer colour than 

 the same silk dyed by the same process in Coventry? 



