M. A. 0. Des Cloizeaux on Amblygonite and Montebrasite. 309 



isolated, have an exceedingly great power of discharging both kinds 

 of electricity. 



The effects in regard to discharge are shown to be similar when 

 platinum wire, rendered hot by a galvanic current, is used, and also 

 when the condensed electricity of a Leyden jar is experimented on. 



As hot iron shows a preferential power of discharging — over 

 + electricity, so it is found that white-hot but isolated iron 

 refuses to be charged either with -f- or — electricity. As the 

 iron cools, it acquires first the power of receiving — , and afterwards 

 of receiving + . Further, while white-hot iron in contact with 

 an electrified body prevents that body from retaining a charge of 

 either kind of electricity, as it cools it permits a + charge to be 

 received, and subsequently a — one. 



A suggestion is made as to the existence of an electrical 

 coercitive force, the presence of which together with its diminu- 

 tion by heat would explain much of what has been described. 



Peb. 20. — Rear-Admiral Richards, C.B., Vice-President, 

 in the- Chair. 



The following communication was read : — 



" Ou a new Locality of Amblygonite, and on Montebrasite, a 

 new Hydrated Aluminium and Lithium Phosphate." By A. 0. 

 Des Cloizeaux. 



A mineral found in 1862 at Hebron, Maine, U. S. A., after a 

 mere tentative examination by Professor Brush, who announced 

 the presence in it of lithia in considerable quantity, resembled the 

 amblygonite of Penig so closely as to lead to its being looked on 

 as amblygonite. The crystalline system and birefriugent optical 

 characters of this mineral were determined by the author in 1863. 

 In 1870 a mineral found in the tin vein of Montebras (Creuse), 

 though resembling the amblygonite of Hebron, appeared to the 

 author to differ from it so far as to justify his designation of it 

 under the name of Montebrasite. Towards the close of 1871 

 he received another specimen from Montebras, which presented all 

 the characters of the American amblygonite, and which conse- 

 quently was easily distinguished from the montebrasite. Subse- 

 quently, analyses by Pisani, v. Kobell, and Rammelsberg, and 

 optical observations by the author, proved the identity of the 

 montebrasite of Montebras with the amblygonite from Penig. 

 But this is not the case with the amblygonite from Hebron, nor 

 with that from Montebras, which had been analyzed by Pisani. 

 These differ from the amblygonites of Saxony and Moutebras (which 

 last he had previously named montebrasite) by the absence of 

 soda, by the preponderance of lithia, and the presence of a notable 

 amount of water, while at the same time they contain almost equal 

 proportions of phosphoric acid and alumina. 



The differences which these two minerals present iu their 

 physical and chemical characters are sufficiently decided to com- 

 pel our treating them as distinct species. The name amblygonite 



