ZOOLOGY AND BOTANYj MIOROSCOPY, ETC. 525 



is kept constant by employing fluids of a definite^ boiling-point, as regards 

 the required amount of heat, instead of a water-bath. 



A double-walled vessel (fig. 1 64) contains the heating fluid e between 

 the two walls, the object to be heated being within the 

 inner chamber /. A tubular opening h in the top of Yiq 154 « 



the vessel carries a glass condensation-tube c for 

 cooling the reflux air. Air-tubes a enter the dry 

 chamber from below, and the cover has an opening 

 d, which is closed by a slide. The apparatus is only 

 intended by the inventor for high temperatures, but 

 it will undoubtedly be easy to adapt it to the wants 

 of microscopists for the use of fluids boiling at lower 

 temperatures. The quantity of gas used is very small, !( 



a very small jet only being required to keep the fluid , '^'^ jjj. 



' Drying Apparatus for the laboratory.* — Herr tt! | '^jllHB 



H. Eohrbeck has devised a drying apparatus which, "^"ffll ||n ^Bl 



by taking advantage of the circulating property of hot Hiife- I^^H 



air, and by the adoption of a chamber for heating the Hi |p|!fe_JW| B 



air previously to its admission to the drying closet, mP?'*i?SfBHw 



is able to preserve an equable temperature in the ^jb Se-:^! ^^^^ 



The apparatus, apparently, consists of a double 

 walled case, five sides of which are protected by an asbestos layer. The 

 internal chamber is surrounded by an interspace for the circulation of the 

 exit air, while beneath its floor is situated a preliminary heating chamber 

 subdivided into an upper and a lower compartment. The lower compart- 

 ment is heated directly from beneath by a flame. From here the heated 

 air ascends to the upper compartment, whence it finds its way through 

 fenestrations to the dry chamber, out of which it passes to the interspace. 

 Thus the dry closet is surrounded by warm air. The draught can be 

 regulated by means of valves. The apparatus is closed by a double door 

 and is provided with the usual thermometer and regulator. 



Micro-chemical Analysis of Minerals-t — Dr. T. H. Behrens gives a 

 description of methods used for the analysis of small fragments of minerals 

 with the aid of the Microscope, based on the detection of the various con- 

 stituents by conversion into various compounds, the crystallographic 

 forms or appearance of which are well known. 



The mineral is dissolved in hydrofluoric acid, or an acidified solution 

 of ammonium fluoride, and the fluorides converted into sulphates imder 

 such conditions that the fluosilicates and fluoaluminates only remain un- 

 altered. Then in the concentrated solution obtained the calcium is 

 detected in the form of sulphate, the potassium as the platinochloride, 

 sodium as a double sulphate of cerium and sodium, lithium as sulphate 

 after separation of the calcium sulphate, and barium and strontium also 

 as sulphates. The double phosphate serves to indicate the presence of 

 magnesium, and an alcoholic solution of alizarin that of aluminium. For 

 the detection of chlorine, mercurous is preferable to silver chloride ; for 

 fluorine the best reagent is sodium chloride, the fluoride being previously con- 

 verted into a silicofluoride. Test analyses are given, which were made with 

 • 0002 gram of tourmaline, of an apophyllite, a boracite, and other minerals. 



* Chem. Ztg., 1885, No. 21. Cf. Bot. Centralbl., xsvi. (1886) pp. 313-5. 



t Eec. Tray. Chim., v. (1886) pp. 1-33. See Journ. Chem. Soc, Lond.— Abetr., 



(1886) p. 917. 



