PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 633 



carbon and hydrogen that they form the homologous hydrocar- 

 bons, which can be obtained from wood by distillation. Light, in 

 the case of iodide of silver, may have the power of doubling the 

 number of elemental atoms in a compound atom, and as the num- 

 ber of such compound atoms is only half of that of the original 

 compound atom, the total amount of iodine ami silver in such a 

 body would remain the same. 



The remarkable action of silver haloids m:iy depend somewhat 

 on their typical equivalence, and still more on the numerical rela- 

 tions of their atomic v/eights. Silver is the only common metal 

 regarded as mon-atomic. In this respect it resemlrles the four 

 halogens, and differs tVom all the metals except those of the alka- 

 line class. The atomic weight of silver is equal to the difference 

 between that of the lightest and heaviest halogen. Both the 

 element, iodine and the salt, liuoride of silver, are on the hydro- 

 gen scale, respresented by the number 127. 



Looking in another direction, wo notice that an atom of silver 

 weighs just nine times as much as one of carbon, -which is classed 

 among the tetratomic elements. Numerous compounds containing 

 carbon and chlorine are wonderfully sensitive to light; and, it may 

 not be too presumptuous here to predict, that among thera may 

 hereafter be found, a substitute for the silver salt. 



COLLOSSAL LabORATOPJES, 



The Prussian government, fully aware of the great national 

 importance of chemistry, has given orders that two immense 

 chemical laboratories shall be erected, one at Berlin, and the other 

 at Bonn, under the direction of Professor A. W. Hoffmann, the 

 distinguished chemist and author, who has until lately resided and 

 lectured in London. The building and court at Bonn occupies 

 about 44,000 square feet. It adjoins the Botanical Garden, and is 

 near the Universit}'. The basement contains, besides store rooms, 

 the rooms for metallurgical and other operations requiring large 

 quantities of fuel, those for medico-legal and chemico-physiological 

 research, &c. All the remaining spaces intended for educational 

 purposes, viz : the laboratories with their adjoining rooms for 

 esjtecial operations, and side-rooms, balance-rooms, rooms for 

 volumetric analysis, combustion rooms, lecture theaters, museums 

 of specimens, the study and private laboratory of the director 

 and the apartments of assistants are, one and all, on the ground 

 floor. 



