MANIPULATION. 43 



acid to make a concentrated solution. The mixture will absorb the 

 oxygen and rise in the vessel. Where practicable it is a good plan to 

 place the pyrogallic acid in the closed space (see page 97;. The method, 

 of course, also gives the amount of oxygen contained in a given vessel. 

 Or, the use of phosphorus, as described in the preceding paragraph, also 

 accomplishes this end, but it cannot be used with moist seeds, for it in- 

 jures these. 



To Render Thread Non-hygroscopic. Use a silk thread and thor- 

 oughly wax it by drawing it several times o^er a lump of beeswax; this 

 will render it nearly but not entirely non-hygroscopic.* 



To Transfer Tubes, etc., with Open Ends in Liquids to Other Liquids. 

 Prepare a small dish (as the lower end of a vial, removed by the method 

 earlier described) large enough to fit easily over the lower end of the 

 tube; fasten to it a. wire handle; slip the dish beneath the end of the 

 tube, and lift it from the liquid ; it will be sealed from air by the liquid 

 of the dish, and may thus be lowered into the new liquid, and the dish 

 removed. 



To Keep Chemicals Pure. Make it a rule never to pour back chemi- 

 icals into the bottle from which they were taken. 



To 2\emove Stuck Glass Stoppers from Bottles. If the top of the stop- 

 per is flat, it may be placed in the hinge-crack of a door partly closed 

 upon it, when a gentle turning of the bottle often loosens the stopper. 

 Or, holding the bottle suspended from the stopper a half inch above the 

 table, tap the stopper with a wooden hammer-handle or equivalent. Or, 

 twist a cotton rag into a spiral roll several inches long, and dip it into 

 boiling water excepting the ends, which are held ; twist it quickly around 

 the neck of the bottle, which swells the neck and usually loosens the 

 stopper. 



To Clean Sediment from a Bottle. Place shot or coarsely crushed 

 glass (fragments of tubing) in the bottle and thoroughly shake and cir- 

 culate it with water. 



To Bore Holes Through Glass. Use the end of a round file ; keep it 

 wet with turpentine and camphor and rotate, using a carpenter's brace, 



* The hygroscopic variation in length of even an unwaxed thread is but slight. 

 I have carefully experimented upon this point with silk sewing-threads a meter long 

 hung in a tube into which moist and dry air could be drawn. The total range of 

 variation in length in an unwaxed thread was 1. 1 cm., that is i.ifo; in a thread 

 waxed in the ordinary way it was .5 cm., i.e. one half of one per cent, while with a 

 thread boiled in wax .85 cm., i.e. .85 of one per cent. Threads of similar length 

 hung in an open room and read carefully during different kinds of weather gave 

 much less variation. Hence in any apparatus in which threads must be used, waxed 

 silk threads give so small an error due to hygroscopicity that it may be neglected, 

 especially if as short threads as possible are always employed. 



