434 RHCORD OF SCIENCE FOR 1887 AND 1888. 



most infusible oxides are probably tbosein wbich the bi<jjhest polymeri- 

 zation is reacbed. 



The aiitbors also connect tbe pbenomena of debydration witb tbe 

 periodic curve, and reacb tbe following conclusions : 



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

 odd members tbe temperature of complete debydration diininisbes as Ibe 

 atomic weight of tbe positive element increases. For even aieuibers tbe 

 reverse is true. 



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

 F, or from K to Br. Here tbe temperature of com])lete debydiatiou 

 seems to diminish from tbe beginning to about tbe middle of the period, 

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

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

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



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

 tween commercial zinc and dilute sul[)liuric acid is I'amiliar to everyone, 

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

 taminated witb sulphur dioxide and sulphuretted hydrogen. Taken al- 

 together the re-actions are somewhat complicated, varying witb 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 tbe comniercial granu- 

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

 especially purified. The acid varied from H2SO4 to H3SO4, IOOH2O aj)- 

 proximately. 



In all the re-actions hydrogen was evolved, and zinc sulphate witb some- 

 times free suli)hur was tbe only solid product. Sulphur was liberated 

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

 than H2SO4, 2H2O, and its separation is always accompanied by evolu- 

 tion of sulphur dioxide and suli)buretted hydrogen; although tbe quan- 

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

 purified zinc was used, hardly any sulphur was set free, but witb ])lat- 

 inized foil it ai)peared in large quantities ; its formation being possibly 

 due to the mutual action of sulphuretted hydrogen and hot sulphuric 

 acid. 



Tbe purer the zinc the smaller become the quantities of sulphur di- 

 oxide and sulphuretted hydrogen evolved at ordinary temperatures, and 

 when tbe acid is so dilute as H2SO4, ISILO, hydrogen is almost tbe sole 

 gaseous product. Tbe proportions of the other two gases vary witb 

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

 inized foil and concentrated acids, sulphur dioxide is generated at 

 a lower temperature than sulphuretted hydrogen, but tbe latter is pro- 

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

 mercial zinc and H2SO4, 2EI20, little sulphur dioxide or sulphuretted 

 iiydrogen appears at 100°; at 105° both gases are i)roduced freely; at 

 180° torrents of tbe latter gas nearly free from tbe former are evolved. 



