./. />. Ha/whins — Formation of Silver Silicate. 31] 



The combination of geological structure and peculiarity of 

 erosion has given rise to three types of topographic outline. 

 1st, the rugged hilly topography of the plicated and metamor- 

 phosed Silurian rock-, an outline in part descended from an 

 existing pre-Cretaceous topography. 2d, a low hilly Carbon- 

 iferous area with many broad-topped hills, especially where the 

 Cretaceous has JU61 been removed. On account of the de- 

 Btructibility, this area is being rapidly degraded and the cafion 

 character of the Colorado is therefore rapidly disappearing, 

 thus destroying the evidence of the recent rejuvenation. 3d, the 

 sharp angular outline of the Imtte and mesa type in the Cre- 

 taceous area which is rendered possible by the nearly horizontal 

 nature of the bedfl and the alternation of hard and soft strata, 

 but which has probably been aided also by the rapid erosion 

 which followed the early Quaternary uplift. 



Art. XL. — On the Formation of Silver Silicate; by 

 J. Dawson Hawkins. 



But very little seems to have been done with regard to the 

 formation of silicate of silver in the wet way. In Gmelin- 

 Kraut'e Inorganic Chemistry, vol. iii, p. 970, the following 

 statement is made : — " A solution of Ag 2 in 2(HF)SiF 4 , evapo- 

 rated to the consistency of a syrup, deposits hydroscopic crys- 

 tals of 2x\gF . SiF 4 -f 4H 2 0. Out of a solution of this compound, 

 ammonia precipitates a yellow basic salt, if added in small 

 quantities. An excess of ammonia precipitates silicate of 

 silver." A like statement is made by Berzelius — Lehrb. d. 

 Chemie ; Dresden, 1836, vol. iv, p. 629. With the exception 

 of a paper by Dr. M. W. lies,* nothing seems to have been 

 done in this direction since then. With regard to the pro- 

 duction of silver silicate in the wet way, Dr. lies merely 

 repeated the above experiment, without making any analysis 

 of the precipitate. 



The method I have used is so simple that it seems strange 

 that it has not been used before. The reaction made use of 



Xa 5 SiO s -f2AgN0 3 =Ag a SiO, + 2XaXO s . 



The solution of Xa,Si0 3 was made by fusing together Xa 9 C0 4 

 and SiO a , and dissolving the mass in water. The amount of SiO a 



* Engineering and Mining Journal, April 19, 1884. 



Am. Jouu. Scr.— Third Series, Vol. XXXIX, No. 232.— April, 1890. 

 21 



