De Lautoue. — On a Diatomaceous Deposit. 301 



your diatoms are floating in the water and flying round and 

 round ; then with an ordinary glass syringe suck up the dia- 

 toms and squirt them into another glass ready for them, when 

 they will fall to the bottom, and may be collected again clean 

 and free from all coarse sand. 



Mr. C. Peach, of Oamaru, has devised a better and more 

 simple plan — one which has the advantage of not running the 

 risk of breaking the valves. Mr. Peach's plan consists in 

 getting a triangular glass dish, which he makes by procuring a 

 triangular piece of glass 4in. to 6in. long and 2in. to 3in. or 

 more broad at the base and iin. at the apex. He cements to 

 the sides and base narrow strips of glass, about -^^in. broad, 

 leaving the mouth open. He holds this dish so that the base 

 is lowest, and puts in a small quantity of the cleaned diatoms 

 and sand, then shakes it gently and taps the trough gently 

 underneath and harder at the base. The sand goes to the 

 lowest part, and the diatoms rise and separate, flowing towards 

 the mouth in the direction given them by the tapping. When 

 w^ell separated it is a very simple matter to pour them into a 

 clean test-tube, and then, when settled down, take up and 

 mount either as a general slide or as a selection. 



Here you must remember, unless you have got rid of all the 

 acid and all the alkali you will have trouble : firstly, the di- 

 atoms will stick to the glass so that you cannot pick them off; 

 secoiidly, they will not take kindly to your mounting-medium, 

 and you will be vexed to find them full of air-bubbles. 



However, we have now got our clean diatoms. Collect some 

 of the clean sediment in a pipette, and let a drop fall on a per- 

 fectly clean slide. Unless the glass is clean the water will 

 not run freely in all directions, and the diatoms will not be 

 equally distributed. You may even find that with all your 

 trouble there is still some sand left. Well, do not mind : this is 

 easily got rid of. Just hold the slide nearly level in your left 

 hand, and tap, tap with the middle-finger nail of the right 

 hand, and you will soon see all the sand collect in a mass at 

 one edge, while the diatoms are distributed evenly all over the 

 slide. This is one of Mr. Stevens's choicest plans, and he 

 deserves credit for its simplicity. 



Now to pick them off. You can do this slowly while it is 

 wet by chasing any specially large diatom to the edge with a 

 bristle, then bringing it out' of the water, letting it dry, and 

 then picking it up ; but I do not recommend this plan. It may 

 be useful for beginners, but it is a waste of time. 



The proper method is to proceed as follows : The diatoms 

 being evenly distributed and the sand at one edge, heat the 

 slide gently over a spirit-lamp to drive off the moisture and 

 dry the diatoms. Put on one side to cool. Then, if you have 

 not already prepared some slides, do so in the following man- 



