300 Transactions. — Geology. 



boiling-point of sulphuric acid is very high, so do not put your 

 test-tube down in a cold place. The next step is to plunge 

 the contents of your test-tube into a flask containing pure 

 cold water. I use a Florence flask for this purpose, contain- 

 ing nearly a pint of water. Pour the boiling sulphuric acid 

 and diatoms (safer to let it cool) into this flask. Do it care- 

 fully. It will make a noise, but will do no harm. Let your 

 diatoms settle to the bottom, which they will do in a variable 

 time according to their cleanliness and size (twenty minutes to 

 two hours). You must wash them at least four times to get out 

 the acid. The next step is boiling in an alkali. Here we 

 must be careful and not employ too strong an alkali, neither 

 must we boil it too long, or else your diatoms will disappear. 

 It is true that Mr. Morland recommends boiling alternately 

 in H0SO4 and strong liq. potassae to get rid oi refractory 

 dirt in certain instances ; but this is unnecessary here. The 

 cheapest material to use is that recommended by Mr. Stevens, 

 and that is " Hudson's extract of soap"—" washing-powder," 

 as used by our housewives for their clothes. We now pro- 

 ceed, using the Florence flask. Having washed out the acid, 

 add a little hot water to the diatoms, and also about 10 or 

 20 grains of soap-extract^about as much as will cover half an 

 inch of the large blade of your pocket-knife — and boil this — 

 boil it till it boils freely, and stop. Let the diatoms settle. 

 As it cools shake it occasionally to disentangle any diatoms 

 that ]nay be entangled in the scum, and fill the Florence 

 flask up with pure hot water. Some of the debris, &c., re- 

 iTioved by the soap-powder will rise to the top and some will 

 be held in suspension by the water, the diatoms remaining 

 at the bottom. You will now require three or four washings 

 in pure water to get rid of your alkali, and you may now^ take 

 a little up with a pipette and examine it under the microscope. 

 You must not be disappointed if you find it still full of dirt, 

 and sand, and debris. You may find one or two clean enough 

 to pick off and mount, but there will not be many. 



This is the whole process of cleaning so far as chemicals 

 are concerned, and it n:iust be repeated until under the micro- 

 scope you see the diatoms are free from the minute grains of 

 sand which spoil them. You will have to go through this 

 process perhaps a dozen times before they are quite clean, 

 but, having cleaned them, you will be well rewarded for your 

 trouble. 



One great difficulty is to get rid of the sand. Mr. Stevens's 

 plan is to place the cleaned diatoms in a large circular flat- 

 bottomed glass dish — a butter-dish or finger dessert-glass ; then 

 shake them up and rotate them as the digger does to separate 

 his gold-dust. When rotating you will see the sand and large 

 spicules collect in the centre at the bottom of the glass, while 



