SCIENCE-GOSSIP. 



PREPARATION OF DIATOMACEOUS MATERIALS. 



By Edward H. Robertson. 



{Concluded from page \~\.) 



Recent Materials. 



T^7HEN recent and not fossil materials are to 

 be treated, some little deviations are usually 

 observed. As a rule no disintegration is requisite. 

 In every instance they must , however, be treated with 

 hydrochloric acid to remove all traces of calcareous 

 matter. When effervescence has entirely ceased the 

 residue must be well washed. Some persons then 

 submit them to the action of nitric acid only, 

 until finally prepared. In some cases this simple 

 treatment may suffice, but I have found it both 

 expensive and not a whit more effective, and cer- 

 tainly a much more tedious process. Occasionally 

 I adopt this method, and then, first of all, after 

 application of the hydrochloric acid, place the 

 material in a wide-mouthed bottle, pour over it 

 enough nitric acid to cover it, cork and set aside. 

 At the end of, say, three or four days the contents 

 of the bottle will have been resolved into a thick 

 pasty mass, which can at once, if desired, be boiled 

 in a beaker or the Wedgwood vessel. The boiling- 

 point of nitric acid being lower than that of water, 

 great care must be observed not to expose to too 

 great a degree of heat, lest the contents overflow 

 the vessel. I obviate this in the following manner : 

 I have fitted into an ordinary tin saucepan a piece 

 of cork, in the centre of which is a circular hole, 

 into which a beaker may be dropped. About two- 

 thirds filled with water, the saucepan is set on a 

 fire, or oil stove, and the beaker and contents 

 being inserted, it may safely boil until, to make 

 up for evaporation, fresh water or acid has to 

 be added. After two or three hours have elapsed 

 the material must be washed and the process 

 repeated. 



The great drawback to the use of nitric acid is 

 that no sooner does it become even moderately 

 hot than a series of detonations set in, these often 

 being so violent as to cause the containing-vessel 

 to jump bodily, quite a large quantity of the 

 material being sometimes erupted. Nay, occasion- 

 ally, when not carefully tended, I have known the 

 whole contents of a beaker to be, little by little, 

 blown out. This exceedingly annoying experience 

 is entirely obviated when the water-bath is used, 

 as described. The cause of these detonations is 

 that the solid contents of the vessel in use gravitate 

 to the bottom, particularly if much sand or other 

 mineral substance be present. The layer thus 

 formed interposes a moist stratum, and the steam 

 generated beneath or therein finds violent vent 

 into or through the liquid above. 



Bichromate of Potash Method. 



Many of the most successful preparers of 

 diatomaceous materials employ this method. It is 

 simple enough, and efficient where much organic 

 matter is present in the earth to be operated upon. 

 After treatment with hydrochloric acid, being 

 well washed and allowed to subside, all water 

 should be carefully poured off, and, in its place, 

 about three times the bulk of material should be 

 added of sulphuric acid. Bichromate of potash 

 in powder should now be thrown in, and gently 

 stirred with a glass rod. Sometimes considerable 

 ebullition ensues, and the contents are liable 

 to overflow the vessel unless care be exercised. 

 Usually, however, the action is feeble, and 

 bichromate in small quantities may be added until 

 it ceases, when the vessel and its contents may be 

 submitted to heat, more vigorous ebullition then 

 taking place. Whatever the colour of the material 

 when first treated, it quickly assumes an olive-green 

 hue. When all action appears to have ceased the 

 preparation should be poured into a vessel containing 

 a large quantity of pure rain-water, gently stirred 

 and allowed to settle. After well washing very 

 little sediment remains, beyond diatoms, sponge 

 spicules and sand. That is to say, in theory, this 

 should be so ; but, as a matter of fact, I almost 

 invariably find that the process has to be repeated, 

 sometimes more than once. Experience alone 

 will enable the amateur to decide upon the method 

 he elects to practise. I must frankly say that I 

 prefer the chlorate to the bichromate treatment ; 

 and should the reader do the same he wiil find 

 that, with occasional modifications, he may pro- 

 ceed very much as in the case of fossil earths, 

 already described. Let him, however, bear in 

 mind that by the use of the bichromate he escapes 

 explosions and decrepitation, which are somewhat 

 alarming to a nervous person. 



Use of Liquor Potassa. 



As this chemical is often very injudiciously 

 employed in the preparation of diatomaceous 

 materials it will be better to devote a section to the 

 subject. Let me at once say that it should be used 

 as seldom as possible. When, however, all the 

 means already indicated fail to reduce the material' 

 to be disintegrated to an almost impalpable 

 powder, the supernatant liquid should be poured off 

 and enough liquor potassa to cover the solid matter 

 added, and brought to a boil. The boiling should 

 not be continued for more than one or two minutes, 



