Zinc, as a Covering for Buildings. 249 



It is alledged that k poisonous suboxide of zinc is dissolved in the 

 water, which renders it unfit for cooking, and impairs its properties 

 for washing. On this point I have consulted the ablest rrjodern 

 writers on chemistry, Brande, Turner, Thomson, Berzelius, and 

 others. The oxides of zinc seem not to have been much studied. 

 The principal one known, and perhaps the only one certainly known, 

 is the white oxide, (sometimes called the flowers of zinc,) which is 

 quite insoluble in water, and hence could not vitiate its properties. 

 Berzelius thinks there are two others, the suboxide and the super- 

 oxide. 



The suboxide is the gray coating formed on the surface of zinc 

 by exposure to the weather, and this is. the substance which, it is 

 said, is dissolved and mixed with the water, which falls from a zinc 

 roof, thereby impregnating it with deleterious properties. This opin- 

 ion, so far as I can learn, is unsupported by any writer on chemistry. 

 Turner says, " zinc undergoes little change by the action of air and 

 moisture." Aikin's Chemical Dictionary, a work of merit and au- 

 thority, says, " the action of the air upon zinc, at the common tem- 

 perature, is very slight: it acquires a very thin superficial coating of 

 gray oxide, which adheres to the metal and prevents any further 

 change." The statement of Thomson is, that zinc, when exposed 

 to the air, soon loses its lustre, but "scarcely undergoes any other 

 change.'''' The account given by Berzelius, the ablest chemist of 

 the age, is very explicit and much to the point. He says, " this 

 oxide is formed on the surface of zinc which remains a long time 

 exposed to the contact of the air. It has a dark gray color when 

 moistened, but by drying becomes of a light gray. Ordinarily it 

 forms a thin crust on the surface, which neither increases nor expe- 

 riences any change in the air ; but acquires great hardness, and re- 

 sists, better than the metal itself, the mechanical and chemical action 

 of other bodies. A piece of zinc sufficiently suboxidized at the sur- 

 face, dissolves with extreme slowness in the acids, and only at the 

 boiling temperature ." 



Such are the opinions of chemists, and particularly of Berzelius, 

 whose unrivalled skill and accuracy in chemical analysis, have been 

 the admiration of all cotemporary chemists. 



The opinion of Dr. G. is considerably at variance with those now 

 adduced. I think he has not stated very fully, and certainly not very 

 satifactorily, the reasons on which it is founded. He mentions, how- 

 ever, as a proof that this suboxide is dissolved in water from zinc 



Vol. XXXI.— No. 2. 32 



