434 RKCOUD OF SCIENCE FOR 1887 AND 1888. 



most infusible oxides are probably those in which the highest polymeri- 

 zation is reached. 



The authors also conuect the phenomena of dehydration witli the 

 periodic curve, and reach the following conclusions : 



(A.) As regards oxides belonging to the same group. In the case of 

 odd members the temperature of complete dehydration diminishes as the 

 atomic weight of the positive element increases. For even members the 

 reverse is true. 



(B.) As regards oxides belonging to the same period, as from Li to 

 F, or from K to Br. Here the temperature of comi)lete dehydration 

 seems to diminish from the beginning to about the middle of the ])eriod, 

 and then to increase as we approach its end. To this rule there are 

 only three apparent exceptions, and to the former rules there are none. 

 (Journ.Chem. Soc.,liii, 59.) 



The interaction of zinc and sulphuric acid. — The ordinary reaction be- 

 tween commercial zinc and dilute sulphuric acid is familiar to every one, 

 and it is also well known that the hydrogen evolved is sometimes con- 

 taminated with sulphur dioxide and sulphuretted hydrogen. Taken al- 

 together the re-actions are somewhat complicated, varying with different 

 qualities of zinc and different concentrations of acid. An interesting 

 qualitative study of the problem has been made by Muir and Adie, who 

 used six different forms of zinc, ranging from the commercial granu- 

 lated metal, through re-distilled zinc, to jdatinized zinc foil and zinc 

 especially purified. The acid varied from H2SO4 to H2SO4, IOOH2O ap- 

 proximately. 



In all the reactions hydrogen was evolved, and zinc sulphate with some- 

 times free suliduir was the only solid product. Sulphur was liberated 

 only at relatively high temperatures, and by acids not less concentrated 

 than II2SO4, 2II2O, and its separation is always accompanied by evolu- 

 tion of sulphur dioxide and sul[)huretted hydrogeu ; although the quan- 

 tity of the latter was sometimes extremely small. When the specially 

 purified zinc was used, hardly any sulphur was set free, but with plat- 

 inized foil it appeared in large (juantities ; its formation being i)ossibly 

 due to the mutual action of sulphuretted hydrogen and hot sulphuric 

 acid. 



The purer the zinc the suuxller become the quantities of sulphur di- 

 oxide and sulphuretted hydrogen evolved at ordinary temperatures, and 

 w^hen the acid is so dilute as H2SO4, 12H2O, hydrogen is almost the sole 

 gaseous product. The proportions of the other two gases vary with 

 purity of the zinc, concentration of acid, and temperature. With plat- 

 inized foil and concentrated acids, sulphur dioxide is generated at 

 a lower temperature than suli)huretted hydrogen, but the latter is pro- 

 duced the more freely of the two when the acid is dilute. With com- 

 mercial zinc and H2SO4, L'HaO, little sulphur dioxide or sulphuretted 

 hydrogeu appears at 100°; at 165° both gases are produced freely; at 

 180^" torrents of the latter gas nearly free ipm the former are evolved. 



