Progress of Invention. 229 



hides, and the completeness with which the air is excluded. As 

 hides prepared in this way require somewhat more bark in tanning, 

 the leather they afford is of a very superior quality. 



Oxidation op Fat Oils by the Action of the Atmosphere. — It 

 has long "been known that fat vegetable oils, when exposed to the 

 air, thicken, and become more or less hard, by absorbing oxygen ; 

 the amount and rapidity of the effect produced on them being 

 greatly modified by the temperature, and the degree of exposure to 

 light. M. Cloez, having made numerous experiments on the precise 

 effects of heat and light, has added considerably to the very large 

 amount of knowledge we have obtained regarding these oils from 

 the researches of Chevreul and other able and indefatigable investi- 

 gators. M. Cloez examined four kinds of oil — two non-siccative and 

 two siccative ; the former being sesame and castor oils, and the latter 

 poppy and linseed oils. He endeavoured, by every possible precaution, 

 to render the conditions of the different experiments exactly simi- 

 lar, so that perfectly reliable comparisons might be made. The 

 exposure to air, in every case, continued for 150 days ; in some of 

 the experiments white, in others coloured light was admitted to the 

 oil, in others light was entirely excluded ; and the augmentation 

 of weight was noted at different intervals. It was found that for 

 thirty days the oil exposed in white glass increased rapidly in 

 weight ; that it increased nearly to the same extent in blue glass ; 

 very little in red or green glass ; and not at all in darkness. After 

 thirty days the increase in weight was greater with blue than with 

 white glass ; and after a longer or shorter period the increase was 

 greater with red and green, than with white and blue glass. After 

 some time, the rapidity with which the weight augments becomes 

 greater : after 120 days the augmentation with poppy oil was 

 found to be about double what it had been after 60 days ; but after 

 160 days it was more than trebled. Heat greatly modifies the 

 effects of exposure. When linseed oil was heated for six hours to 

 100° Cent, in a water-bath, in a current of atmospheric air, notonly 

 was the weight increased, but vapours of a suffocating odour were 

 produced. It is an important fact connected with the art of 

 painting, that the oxidation may be very much accelerated without 

 the application of heat, by the addition of a small quantity of oil of 

 the same kind, which has been previously thickened by exposure to 

 the atmosphere. Oil for painting may therefore be prepared so as 

 to be perfectly colourless, and consequently to produce no diminu- 

 tion of the brilliancy of the colours. 



Illuminating Gas prom Vegetable Refuse. — The utilization of 

 the refuse left after the making of cyder and perry is now being 

 very successfully effected in France. It had been hitherto good 

 for nothing, and in some cases was a source of actual inconvenience 

 and loss. The same thing is more or less true of the waste left 

 from the apples and pears after making cyder and perry in these 

 countries. This otherwise worthless material is now employed in 

 the manufacture of an illuminating gas of most excellent quality, 

 its light-giving power being of a high order, and its combustion not 

 in the least injurious to painting or gilding, since it contains no 



