November, 1841.] \2<j 



O 8) is placed separately on the same shelf under a glass box of 

 the same size as to base, but of only half tiie height of the former, 

 and containing of course 50 cubic inches. To represent the com- 

 bination of these gases to form water and to indicate the amount of 

 condensation which takes place, the oxygen type is taken from 

 under its own box and placed with the hydrogen type beneath the 

 glass box of 100 cubic inches, the 50 inch box being at the same 

 time removed from the frame. There is then seen the sum of the 

 weights of the constituents of water (9), and the bulk of the vapour 

 of water, the same as that of the hydrogen which had entered into 

 its composition. To convey the impression that the product is a 

 liquid, the resulting combination of atoms is carried from the upper 

 to the middle shelf, without being accompanied by the volume-cube. 



The advantages found to result from this method of illustration 

 over those hitherto in use were stated to be the saving of much 

 time and labour, in writing out diagrams and making drawings, 

 and the avoiding of inconvenience of working at a black-board to 

 give after all but an imperfect impression of the truth to be con- 

 veyed. An effect of not less importance was derived from appeal- 

 ing to different faculties at the same time. 



To some minds the bulk of a body conveys a far more distinct 

 impression of its weight than the figures which represent that 

 weight. In the method now exhibited, both these modes of appeal- 

 ing to the mind and memory are united. The colour of many of 

 the substances combined with the bulk with the symbols which 

 represent them and with the figures which expi-ess their weight, can 

 hardly fail to fix a lasting impression on the mind of every student 

 in chemistry. To these maybe added the facility of making appa- 

 rent by direct juxtaposition the relation by weight and by volume 

 of the constituents of all gaseous mixtures. 



The application of this apparatus was shown in exhibiting the 

 composition of the oxides and other minerals. 



The views of M. Liebig in regard to the composition and true 

 radical of Phosgene gas, carbonic acid and oxalic acid, were also 

 displayed. 



The constitution of ammonia, of atmospheric air, of nitrous- 



20 



