382 Progress of Invention. 



which, the effect is due has been actually obtained. Mere compression, 

 by squeezing out this gas, destroys the amalgam, leaving a film which 

 has the appearance of lace, on accounb of the space which the 

 bubbles of hydrogen had occupied ; and finally the formation of the 

 amalgam depends on its capability of being swollen up by the gas, 

 since the more fluid the sodium amalgam the more effective it is in 

 producing the supposed amalgam of ammonia. The question 

 regarding the nature of ammonia is more important even than, at 

 first sight, it would seem ; since, if ammonia is the oxide of a metal, 

 we may fairly conclude that many other of the metals, if not all of 

 them, are compound bodies ; and if they are compound, it must be 

 possible to form them artificially ; in which case the alchemists were 

 not the visionaries they have so long and generally been con- 

 sidered. 



Economic Productions of Pyrogallic Acid. — In practice only 

 twenty-five per cent., or one third of what might be expected from 

 theory, of pyrogallic acid is obtained from gallic acid. This loss, 

 from the imperfection of the process employed, is very serious, as 

 the quantity of pyrogallic acid now used, especially by photo- 

 graphers, is great. Attempts were made by various chemists of 

 great eminence to prevent this waste, but with only partial success, 

 until M.M. Victor de Luynes and Gr. Esperandieu devised the im- 

 provements, which they have recently brought under the notice of 

 the Academy of Sciences. The waste which occurs with the ordi- 

 nary process arises — as it often does in similar cases — from decom- 

 position occurring" at the very temperature required for production, 

 and is therefore proportional in amount to the time required for the 

 manipulation. It is avoided by the method of M.M. de Luynes and 

 Esperandieu, who decompose the gallic acid, by subjecting it to the 

 action of bases, or even of pure water, in close vessels. They intro- 

 duce the gallic acid, along with two or three times its weight of 

 water, into a bronze boiler, and heat it to between 200° and 210 J 

 Cent. Having kept it at this temperature for about half an hour? 

 they allow it to cool ; then boil the resulting pyrogallic acid, which 

 is almost colourless already, with animal charcoal, filter, and evapo- 

 rate at an open fire, to drive away the water. On cooling, amber 

 or rose-coloured crystals are formed — they would be white if the 

 distillation had been effected in vacuo. The quantity of pyrogallic 

 acid obtained in this way is fully equal to that which theory would 

 lead us to expect ; and the quality is quite as good as that ordinarily 

 obtained by sublimation. This method was first used by Pelouze, 

 but was not, until now, applied to commercial purposes. 



Light as a Source of Motion. — Although it has been known 

 for some time past that light is capable of producing mechanical 

 effect, the amount of this effect was unknown ; it has, however, 

 been determined by Professor Thomson of Copenhagen, by changing 

 the light into heat, the mechanical effect of which is easily calculated. 

 To free the beam of light, which he examines, from all calorific rays, 

 he passes it through a layer of water ; and, when it is afterwards 

 transmitted to the thermo pile, the deflections of the needle aecuratelv 

 indicate its heating power. During these experiments certain dis- 



