380 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
with 30 parts water. The two fluids are then mixed and strained. The 
glycerin is next added, and finally the thymol dissolved in alcohol. 
Test for the Production of Indol by Bacteria.* — Dr. Th. Smith 
claims that dextrose-free bouillon is the best medium for testing the 
production of indol by bacteria. It is prepared from beef infusion, 
by extracting either in the cold or at 60° C., and inoculated the same 
evening with a culture of an acid-producing bacterium, such as B. coli , 
and placed in the thermostat. Next morning the infusion is boiled, 
filtered, pepton and salt added, and then neutralised and sterilised. 
Method for Splitting up Argillaceous Silicates containing Diatoms t 
— Herr G. Marpmann communicates a method for obtaining diatoms 
from schist and argillaceous earths. It consists in treating the earths or 
clay with potassium pyrosulphate. The chemical reaction is represented 
in the following formula. 
Al 2 (Si0 3 ) 3 + 3K 2 S 2 0 7 = A1 2 (S0 4 ) 3 + 3K 2 S0 4 + 3Si0 2 . 
In this way are formed easily soluble sulphates of aluminium and 
potassium, while the silicic acid, for the most part in condition of quartz 
or diatom shells, is not affected, though some of it remains in a soluble 
state. 
In practice the procedure is as follows. 
One part of the broken up clay or earth is heated with three parts 
of the salt, and when melted, one or two parts more of the salt are added. 
When thoroughly melted, the mass is poured out into a vessel filled with 
water, and then boiled for a time. If the mass do not thoroughly dis- 
solve, the sediment should be treated with strong hydrochloric acid, and 
then the diatoms separated by fractional sedimentation. 
The salt (pyrosulphate) may be made by heating 87 parts of neutral 
sulphate of potash in a platinum dish with 49 parts of pure sulphuric 
acid. When thoroughly melted, the mass should be poured out on to a 
dry porcelain plate, and, when cold, broken up and preserved in stoppered 
bottles. 
Making Sections of Steel.} — Mr. F. S. Eice prepares sections of 
steel for the purpose of demonstrating the microstructural character- 
istics. The pieces should 3/4 in. in diam. Sections should be 3/16 in. 
thick, if they are to be heated after cutting in the lathe. The best 
sections are obtained by carefully grinding off the surface to a plane 
by hand on an ordinary quick-cutting oil-stone, then on the finest 
Belgian oil-hone, and finally polishing on a piece of chamois tightly 
stretched over a block of wood and charged with peroxide of tin. 
When thoroughly polished, the surface is washed with alcohol followed 
by a little chloroform. The polished surface is then etched in order 
to develop the structure. 
Though this can be done by means of nitric acid and water, the 
surest and most delicate results are obtained from a saturated solution 
of iodine in alcohol diluted with an equal bulk of alcohol, both 95 per 
cent. Several applications of the iodine solution may be required. 
After each etching, wash in 95 per cent, alcohol, and dry quickly to 
* Journ. Exper. Med., ii. (1897) pp. 543-7. 
t Zeitschr. f. angew. Mikr., iii. (1898) pp. 341-5. 
t Trans. Amer. Micr. Soc., xix. (1897) pp. 28-42 (3 pis.). 
