490 



PHYSICAL GEOGRAPHY. 



spirit-lamp, and, to support the vessels he employs, has a little metal 

 arrangement on the top of the chimney, such as is supplied for the pur- 

 pose of holding a small tea-kettle and the like. The only objection to 

 the oil-lamp is, that, unless the wick be well turned down, we are liable to 

 have our vessels blackened. However, the heat given off by burning 

 petroleum is very great, and I have often used such a lamp with advan- 

 tage. If desired, of course, the source of heat used may be gas, burned 

 in a Bunsen's burner, or a spirit-lamp ; and this last, especially if it be 

 supplied with a metal chimney to cut off draughts, is, all things consid- 

 ered, the best, as it is very cleanly, not being hable to smoke the bottom 

 of the glass or porcelain vessels used. If we are going to work with 

 large quantities of material, we shall require a small sand-bath to heat 

 the glass vessels upon. In small quantities, the diatoms may be boiled in 

 test-tubes, when some sort of holder will be required. The metal ones, 

 sold by dealers in chemists' apparatus, are extremely handy ; but I have 

 found that we can make very good ones out of old paper collars. One of 

 the kind called "cloth-hned" may be cut into strips about three quarters 

 of an inch wide and three inches long. Such a strip is folded around 

 the test tube, near the top, and the ends, brought together, are held 

 between the fore-finger and thumb. In this way the tube is firmly 

 grasped, and can be held over the lamp without much danger of burning 

 the hand, as the paper collar strip is a bad conductor of heat; or, the 

 paper strip may be grasped in an "American clothes-peg," which has a 

 spring to force its parts together. Large quantities of diatoms are best 

 boiled in porcelain evaporating-dishes, glass flasks, or beaker-glasses. 

 The last mentioned vessels are also by far the best things for washing 

 them in. A few, say three or four, glass stirring-rods will be found 

 useful ; and one or two American clothes-pegs to take hold of hot evap- 

 orating-dishes with. Then there will be required a few dip-tubes, made 

 of small glass tube, drawn out over a flame, so that the opening is con- 

 siderably diminished. The mode of making these cannot be given here, 

 but will be found in books on chemical manipulation ; and it will be well 

 for the student to learn to make his own dip-tubes, as a number will be 

 required first and last, and they are easily broken. Of course there will 

 be required a number of glass slides, of the usual dimensions of three 

 inches by one. These should be of as white glass as possible, and it will 



