﻿132 E S. Dana — Crystallization of Gold. 



When the above method was first under trial, and it was not 

 known how much the deposition of the steel gray film was 

 influenced by foreign substances, the course of procedure was 

 as follows : 



The arsenious liquid under examination was placed in a bu- 

 rette and fed from this into the capsule containing hot chlor- 

 hydric acid and a copper square. After the exhaustion of the 

 arsenic by the successive introduction of squares, the burette 

 was filled with a standard solution of As 2 3 (1 : 10,000), and 

 this solution fed into the same liquid until the same number of 

 squares were covered. The amount of arsenious oxide was 

 then read directly from the burette. Theoretically superior, 

 the results hardly excel in accuracy the results of the preceding 

 method, while the time and care required are greater. 



As a matter of curiosity it may be stated that a copper 

 square one mm. on a side is capable of disclosing and estimat- 

 ing -0000025 grm. arsenious oxide, a quantity four hundred 

 times less than that necessary for turning the beam of the ordi- 

 nary chemical balance. 



The above quantitative method is commended for trial as being 

 in the hands of experts free from fallacy ; requiring few chemicals 

 and utensils ; not interfering with the search for other organic 

 poisons and not interfered with by ordinary impurities, and as 

 intelligible to the ordinary juryman, notwithstanding the quib- 

 bles of counsel. 



Brunswick, Me., April 19, 1886. 



Art. XV. — On the Crystallization of Qold ; by Edward S. 



Dana. 



The attention of the writer has been directed recently to 

 some specimens of crystallized native gold offering several 

 points of interest and novelty. The crystallization of the 

 native metals, gold, silver and copper, is a subject of more 

 than usual difficulty, and for our knowledge in this direction 

 we are largely indebted to the excellent work of Eose.* More 

 recently vom Eath has made an important contribution in 

 regard to the complex crystallized plates and thread-like forms 

 of gold; Helmhackerf has described the interesting gold crys- 

 tals from Sysertsk;^: while v. Jeremejew,§ Lewis,] Fletcher^" 

 and Werner** have added to the list of observed forms. 



* Pogg. Ann., xxiii, 196, 1831 ; Reise nach dem Ural, i, 198, 1837, et al. 

 f Zeitsch Kryst., i, 1, 1877. % Tschermak's Mineral. Mittheilungen, 1877, 1. 

 § Yerh. Min. Ges. St. Petersburg, II, v, 402, 1870. 

 I Phil. Mag., v, iii, 456, 1877. \ Ibid., ix, 1880. ** Jahrb. Min., i, 1, 1881 



