A manual of microchemical analysis / by H. Behrens ; with an introductory chapter by John W. Judd.

Date:
1894
Catalogue details

Licence: Public Domain Mark

Credit: A manual of microchemical analysis / by H. Behrens ; with an introductory chapter by John W. Judd. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    (8) Chemical methods of separation have frequently been employed with great success. Weak or dilute acids serve to remove the calcium carbonate from silicates, and boil- ing acid will separate the magnesium carbonate. By the use of strong hydrochloric acid, basic and hydrous silicates may be decomposed, and the normal and anhydrous ones left behind. Students of meteorites have long employed this method for separating olivine from enstatite. By the use of hydrofluoric acid either as a gas or in solution, most of the silicates may be decomposed ; and in some cases hydro- fluosilicic acid or ammonium fluoride may be employed instead of the more powerful but dangerous acid. Mixtures of hydrofluoric with hydrochloric or sulphuric acids decom- pose nearly all silicates, and in this way rutile, zircon, tour- maline, spinel, andalusite, sillimanite or kyanite, which are not so decomposed, may be isolated from the rocks in which they occur. By treating powders with alkaline solu- tions, or by fusion with alkaline carbonates, certain con- stituents may be decomposed or dissolved while others are left intact. Fouque has shown that by the judicious use of hydrofluoric acid on a powdered rock, first the glassy ground-mass, next the felspars and similar constituents, then the quartz, and finally the ferro-magnesian silicates, are attacked. In this way it has been found possible to isolate from rocks the various porphyritic crystals, preserving their forms and even their brilliant crystalline faces. If the process be skilfully carried out, the most admirable results may be obtained by this method.1 There are other chemical methods which are possible in certain cases which will readily suggest themselves to the petrographical investigator. A very valuable synopsis of all the separation 1 MfSnioircs pn5scnt<5s par divers savants a l'Academie des Sciences