682 SUMMARY OF CURRENT RESEARCHES RELATING TO 



of fibrous calcium carbonate, was boiled for half an hour with cobalt 

 nitrate solution. Afterwards the slice was mounted, polished side down, 

 and ground down till transparent. It was found that the (aragonite) 

 corals, gasteropoda and Halimeda were stained red, while the (calcite) 

 echinid spines were unaltered, as was also the cementing fibrous calcium 

 carbonate. 



There was seldom difficulty with calcite and dolomite, but in cases 

 of doubt Lemberg's test was applied. This consists in treating the 

 exposed surface of a thin section for 5-15 minutes with a solution con- 

 taining a mixture of aluminium chloride and hsematoxylin. Dolomite 

 is unchanged, but a deposit of aluminium hydrate forms on calcite and 

 stains reddish-purple. The staining solution is prepared by dissolving 

 four parts of dry aluminium chloride in 60 parts of water and adding 

 six parts of logwood. The whole is boiled and stirred for 25 minutes, 

 and made up to original bulk. The author did not get good results if 

 the stain remained on the rock for more than 15 minutes. 



Red Rain.* — F. Chapman and H. J. Grayson discuss the phenomenon 

 of red rain with special reference to its occurrence in Victoria, and 

 append a note on Melbourne dust. In two samples which fell at differ- 

 ent times, they identified fragments of numerous minerals, diatoms, 

 vegetable tissue and spores, sponge spicules, lorica of a rotifer, and 

 various bacteria. 



The Melbourne dust contained besides fragments of numerous 

 minerals, cosmic dust, greenish-brown glassy spheres, and bits of rotifers 

 and diatoms. 



New Etching Reagent for Polished Steel Sections. f — F. N. Speller 

 suggests the following method of developing the structure of iron and 

 steel specimens. From 2 to 4 c.cm. concentrated nitric acid are slowly 

 run into 100 c.cm. C. P. glycerin and the solution well mixed. After 

 polishing and drying the specimen the surface is treated with a drop of 

 C. P. glycerin, which is gently rubbed on the steel with the tip of the 

 finger. A drop of the etching solution is now applied and friction with 

 the finger continued until the surface is etched to the degree required. 

 By fastening the specimen in a suitable holder the progress of the action 

 of the acid may be -followed through the Microscope and the develop- 

 ment of the structure checked at the proper time by wiping the glycerin 

 off with a soft cloth, and applying a drop of caustic soda-glycerin for a 

 minute. The author states that the process works very well with low- 

 carbon steels, the pearlite and granular structure being sharply defined, 

 while the ferrite remains unstained even after 24 hours' continuous 

 application of the etching solution. The chemical composition of this 

 solution is not positively known, but it probably contains glyceric 

 acid. It is found desirable to prepare a fresh solution every week and 

 to keep in stock solutions of various strengths. The nitric acid used 

 should not be fuming, otherwise nitroglycerin would be formed — a very 

 dangerous substance. 



The Microscope in Crucible Steel Manufacture.^ — J- J- Mahon 

 points out that the Microscope, in order to be of any practical assistance 



* Victorian Naturalist, xx. (1903) pp. 17-32 (2 pis.). 



t Metallographi&t, vi. (1903) pp. 264-5. J Tom. cit., pp. 195-6. 



