Intelliitence and Miscellaneous Articles. 233 



"to 



iodide of lead the nitrate ought to be preferred to the acetate, on 

 account of the greater quantity of product which it yields. 



The process by iodide of calcium is the most advaDtSgeous both 

 as to the quality and quantity of the product. jxayin^ii 



The two processes by iodide of iron and iodide of zinc yielding 

 equally fine and abundant products, it is nearly indifferent which 

 is employed. 



The process by iodide of sodium offers no advantage, and that by 

 iodide of potassium is the least economical. 



There is a loss of nearly 10 per cent, in preparing iodide of lead 

 on using iodide of potassium and acetate of lead ; the greater part 

 of which loss may, however, be avoided by substituting the nitrate, 

 or by adding to the supernatant liquor a sufficient quantity of nitric 

 acid to decompose the acetate of potash. — Journ. de Pharm. et de 

 Chem, Janvier 1849. :;'irnfoi iHBJoq lo a/ajyoc 3uJ ^d i)3vio8?il) 



ON THE PROTOGINE OF THE ALPS. BY M. DELESSE* (' T 



The author observes that protogine usually contains five different 

 minerals, which are, quartz, orthose, oligoclase, mica with a base of" 

 iron, and a variety of talc : these may be seen in the protogine of 

 Mont Blanc. These minerals are not however equally distributed, 

 and one or more of them are frequently wanting ; but then the 

 minerals which remain have so preserved the same characters as 

 those which they possessed when the five elements are present in 

 the rock, that it is impossible not to consider them as formed under 

 the same circumstances ; they constitute therefore varieties of the 

 original rock, into which they pass insensibly, both by their mine- 

 ralogical characters and their geological relations. . 



Quartz. — Quartz forms one of the important elements of proto,- 

 gine as of all granitic rocks. When the rock has a well-character- 

 ized granitic structure, the quartz of the paste is sometimes con- 

 fusedly crystallized ; generally, however, this does not occur, and it 

 is hyaline, gray or violet ; when it is in crystals of several centi- 

 metres in thickness, as seen in some veins, instead of being reddish 

 or violet, it generally has a deepish black colour, and is of the^ va- 

 riety called smoky quartz. (Vkt- Oc ~! 



It may be stated generally that in fracturing pieces havmg the 

 usual thickness of the grains of quartz or the paste of the rock, the 

 difference of colour is derived rather from the greater thickness of 

 the quartz in the veins than from the presence of a greater quantity 

 of colouring matter. i- 



This colour of quartz, which is observable in many granitic rocJ{%> 

 is derived from organic matter, which is volatile without leaving 

 any residue, and disappears completely by slight calcination, the 

 quartz losing only twelve thousandths, and becoming wiu^e^^lld 

 transparent. ; ^.m! - 



Tliis organic matter is not volatile in vacuo at common terapera- 



turesu fox it lioes-not disappear by exposing the q}iSixuiQX:^sf:ysia\ 

 \o noiifiTjsqaiq odJ ai jfirij tsiaamiwqzs badiioaab-avoda adi moil 



