MANIPULATION 249 



LABELS. For bottles. If glass-stoppered, write with pencil on the 

 stopper, and it will show through the neck. Or a colored paraffin pencil 

 made expressly for writing on glass may be used. Or the inscription may 

 be written in waterproof India ink, and when dry covered with Canada bal- 

 sam. Or a paper label may be applied, and afterwards coated thinly with 

 moderately hard paraffin, applied very hot, said to be a most efficient and 

 otherwise satisfactory method. Or a writing diamond, costing about $3.00, 

 is very useful for some purposes. For temporary labelling, druggists' tag 

 labels are most useful. 



MERCURY. Container. See page 50. 



Cleaning may be accomplished sufficiently for most physiological pur- 

 poses by thorough washing in running water carried down through it by 

 a glass tube. Or a continued current of air through it cleans it well. Or 

 it may be allowed to drop through a column of weak nitric acid and subse- 

 quently washed. Compare Detmer, 42, 43. 



Experimenting with mercury should always be done over an indurated 

 fiber saucer, which will catch the leakage. 



OXYGEN. Absorption and Analysis. See page 103. 



Generators. As described in works on Elementary Chemistry. But it 

 is most convenient to obtain it from the cylinders supplied commercially. 



READING GRADUATIONS accurately on thermometers, etc. For 

 this purpose a special magnifier sliding on the tube is supplied by Leitz, and 

 another by Griffin & Sons of Kingsway, London. These instruments 

 could readily be adapted to other accurate readings. 



REGISTERING. For various purposes suitable instruments are 

 described earlier at pages 145, 178, 181, 200, and most of them, especially 

 the Auxograph (page 203), may readily be adapted to other uses. 



Gauges or manometers may to some extent be made registering by drop- 

 ping on the liquid some very fine cork dust, a line of which will be left at the 

 highest point reached. 



Pens for the purpose may be made from glass tubing, or are sold in good 

 forms by the Cambridge (England) Scientific Instrument Company. 



Smoked paper is sometimes used with pointers scratching upon it. The 

 paper is smoked by turpentine burning in a spirit-lamp, and the records may 

 be made permanent through spraying, by an atomizer, with weak gum-arabic 

 solution. 



RUBBER. Boring or cutting is always easier if rubber and instrument 

 are kept wet with water, or, better, with caustic potash. 



Preserving is facilitated by darkness, and in some cases by immersion 

 under water. 



Stoppers with holes may best be sealed by pieces of glass rod smoothed 

 in the flame, or by pieces of sealed glass tubing. 



SIPHONS. Starting without suction. Use a rubber tube and immerse 

 it in the liquid, allowing it to fill; pinch together one end so the air cannot 

 enter; lift this end out over the edge of the vessel and let it fall below the inner 

 level; allow the pinched end to open, when the flow will start. If of glass 

 fill it with water and hold the fingers over the two ends until it is in position. 



