486 Chronicles of Science. [July> 



There are many other forms which might be given to this ap- 

 paratus. Indeed, Mr. Ansell has nearly completed one of a most 

 portable description, which is about the size of an old-fashioned watch. 

 It can therefore be carried into the colliery by the viewer in his 

 pocket, and employed at any moment to determine the amount of 

 dangerous gas present in the air. 



When the diffusion has been completed, that is, when the air 

 within and without the porous septa has become of the same 

 character, the index ceases to move. To restore the index to zero, — 

 which is bringing it back to its normal state, — nothing more is neces- 

 sary than to place it, for a few minutes, in atmospheric air which is 

 free from carburetted hydrogen. 



We have rarely seen a more refined application of science than 

 this, and we cannot but believe it will be found of great practical 

 utility as indicating the presence of fire-damp in collieries, before it 

 becomes dangerous from accumulation. 



In our second Number (April, 1864), we directed the attention to 

 the production of gold from the Quartz veins of the rocks near 

 Dolgelley. 



It appears that at Vigra and Clogau, above 1,600 tons of 

 auriferous quartz have been operated on during 1864, and from that 

 quantity upwards of 11,000 ounces of gold have been obtained. 



The quantities of gold produced in the whole district during last 

 year were as follows : — 



Gold Quartz. Gold. Value. 



Vigra and Clogau .... 1,679 tons, yielding 2,331 ounces, £8,434 

 Cefn Coch ' Welsh Gold Mining Com.) 604 „ 346 „ 970 



Castell earn Dochan ... 29 „ 141 „ 394 



Hafod-y-Morfa, Prince of Wales' Mine . 20 „ 63 „ 176 



Gwynfynydd 4| „ 6 „ 17 



Some very interesting and important experiments are now in 

 progress for the purpose of testing, on a large scale, a discovery 

 which has been recently made by Mr. William Crookes, F.R.S., in 

 connection with the process of amalgamation by which the gold is 

 separated from the other matters with which it is mixed. For a long 

 period, the " sickening " of the mercury, as it is technically called by 

 workmen, has been a source of much annoyance and loss. When 

 sulphur ores, arsenic, bismuth, or tellurium are present, the fluidity 

 of the mercury is destroyed, and it becomes either a tenacious mass 

 or it assumes a powdery character ; in either case, becoming useless. 



Mr. W. Crookes has entirely removed this difficulty by combining 

 a little sodium with the mercury. This preserves the fluidity of the 

 mercury under all circumstances, and, of course, its amalgamating 

 powers. Not merely this, but the sodium amalgam is a preservative 

 against the injurious action of grease in the process. As we have 

 said, extensive experiments are now in progress. Nothing can be 

 more satisfactory than this process appears to be ; but the whole 

 subject is so full of interest, that we prefer waiting until we are 

 furnished with a detailed statement of the results, — which we are 

 promised, — when we hope to devote an article to the consideration of 



