SCIENCE-GOSSIP. 



or the action of this chemical upon the silicious 

 organisms will result not only in the obliteration 

 of their beautiful markings, but very rapidly in 

 their total destruction. The best plan is to pour 

 off into a vessel of cold rain-water the finest sedi- 

 ment which appears so soon as the liquor potassa 

 boils, add a fresh portion to the contents of the 

 vessel, bring this to a boil as before, and repeat 

 until the whole has been disintegrated. If ordinary 

 care be used no injury to the diatoms results from 

 this treatment. 



Preparation of Clays. 



Hitherto I have said nothing about the most 

 refractory diatomaceous materials, such as muds 

 and clays, obtained by dredging, or brought up 

 by anchors, or by the sounding-lead. These it is 

 sometimes almost impossible to prepare with any 

 reasonable prospect of success. Some from vol- 

 canic regions consist mainly of triturated pumice, 

 and after the most careful preparation the few 

 diatoms present are so thoroughly obscured by 

 this substance, which contains from fifty to eighty 

 per cent, of silica, that the operator must either 

 sacrifice the whole, or devote himself with infinite 

 patience to their separation. Then, again, as to 

 the clays. Some of these resist the most insinuat- 

 ing persuasions of the ablest preparers. Popularly, 

 any earth that can be kneaded in the hand like 

 paste is called clay. Strictly speaking, the term 

 means an earth that consists of a mixture of silex 

 or flint, with alumina, usually about three-fourths 

 of the former to one-fourth of the latter. Clays 

 vary greatly in composition, according to the 

 nature of the rocks from whence they have been 

 derived, for they are simply muds formed by the 

 erosion of such rocks. In general they consist of 

 silicaand alumina ; the latter, combined withoxideof 

 iron, gives out an earthy odour when breathed upon, 

 and when dry sticks to the lips if applied to them. 

 The composition of these clays will at once indicate 

 to the diatomist the difficulty of reducing them so 

 far as to enable him to make satisfactory prepara- 

 tions. Where, as commonly happens, calcareous 

 matter is also present, this may be dissolved out 

 by hydrochloric acid ; the coarse sand, if any be 

 present, may be eliminated. The fine silica and 

 alumina, being insoluble in acids, cannot be dis- 

 posed of, except by means that will at the same 

 time destroy the diatoms. The amateur, therefore, 

 should never attempt their preparation until he 

 has acquired considerable skill in the manipulation 

 of more tractable materials. 



General Observations. 



Although I have already referred to the detona- 

 tions that occur when materials are being boiled in 

 nitric or hydrochloric acids, let me here reiterate 

 my warning not to expose vessels containing these 



chemicals to the direct heat of a flame or very hot 

 surface of iron, but to use in preference a water- 

 bath. To reduce the risk of accidents when using 

 nitric acid, it is better, where practicable, to 

 eliminate the coarse sand before boiling. These 

 detonations hardly ever occur with sulphuric acid, 

 but the fumes of this and other acids are most 

 noxious, and the operator should carefully avoid 

 their inhalation. If not convenient to prepare the 

 material by their aid in a place where the fumes 

 may be at once carried up a chimney, then let him 

 operate in some well-ventilated out-building or in 

 the open air. 



As it is not always easy to purchase a large 

 quantity of pure distilled water — and " hard " 

 water should on no account be used — I always 

 collect, when it is heavily raining, in an open 

 situation, as much of the rain as possible, transfer 

 to perfectly clean, clear glass bottles, add a few 

 drops of Condy's fluid, well cork, and set aside in 

 a dark closet until required for use. However 

 clear when collected, a deposit will almost 

 invariably be found at bottom of bottle, after the 

 lapse of a few weeks, sometimes days only. This 

 must not, of course.be disturbed when pouring out 

 the water. I have on hand seldom fewer than 

 from fifteen to twenty quart bottles of this pure 

 rain-water. To be illiberal in its use means to 

 give oneself much more trouble in the long run. 



In using glass rods for stirring the contents of 

 vessels, I prefer those tapering to a point, as the 

 large surface of a blunt rod must inevitably injure 

 some of the finest forms. 



When glass beakers are used to boil materials in 

 acids, and the boiling is vigorous, particles of the 

 scalding contents are commonly deposited on the 

 dry sides of the vessel, with the frequent result of a 

 crack ; hence it is better not to use glass at all, but 

 Wedgwood ware. My pet pipkin has been in use 

 for forty years, during which period my stock of 

 glass beakers has been often renewed. 



From the foregoing remarks it will be seen that 

 there is no mystery in the art of preparing dia- 

 tomaceous materials, but 'the manipulator should 

 ever bear in mind that, whatever he does, he should 

 do thoroughly. There must be no half measures 

 in the preparation of micro-materials. 



In operating with ordinary substances, raw or 

 wrought, blemishes and defects may perhaps be 

 disguised so as to pass muster. It is never so 

 with the minute objects revealed to us by the 

 piercing artificial eye of a microscope. In them 

 the smallest blemish will readily be detected. It 

 therefore behoves the preparer of diatomaceous 

 materials to do his utmost to produce the very best 

 that can be produced, and if, upon examination, 

 the operation appears to have been imperfectly 

 performed, then it must be repeated. 



Woodvillc, Greenhouse Lane, Painswick, Glos. 



