MANIPULATION. 



AIR. Aeration apparatus, aspirator, exhaust, blast; see page 48.- 

 Aeration of closed chambers is usually effective if once daily the old air is 

 blown out (by a puff from the lips). Or a dish of caustic-potash solution 

 in the chamber will absorb the noxious constituent, carbon dioxide. 



Drying may be effected as described on page 158. 



Tightness may be tested by the apparatus described on page 51. 



BLUE-PRINTS. Drawings in black and white may be made from 

 them thus: Go over the dry blue-print, along the desired lines, with water- 

 proof India ink. When dry lay the drawing in a very weak solution of com- 

 mon soda (sal soda). After the blue is gone rinse the print cautiously in 

 water, and then if it shows any yellow stain, put it for a few moments in 

 dilute hydrochloric or sulphuric acid. Wash it in water and dry on a glass 

 plate. Of course one should experiment first upon a valueless print. The 

 ink must be pure and the pen clean. 



BRASS. Corrosion may be removed by immersing the part for a few 

 minutes in concentrated hydrochloric acid. It should then be washed 

 thoroughly in running water and dried over a flame. Finally if touched 

 while hot with a bit of paraffin, this will spread and protect the clean brass 

 from further corrosion. 



CARBON DIOXIDE. Absorption and Analysis. See page 98. 



Generators. See page 52. 



CHEMICALS. Purity is safeguarded by a rigid rule never to return 

 any chemical, even if not used, to its bottle. 



CONNECTIONS. Glass tubing 0} same size. Bring the ends (pref- 

 erably ground square across, or at least smoothed in the flame) together 

 in the middle of a piece of tightly clasping rubber tubing. Where perfect 

 air-tightness is required, the rubber may well be lightly glued, by fish-glue, 

 to the glass, or else may be wired by a single turn of small copper wire twisted 

 up tightly by nippers. If there is pressure from within, it may be resisted 

 by several turns of the inelastic and very adhesive electricians' (or tire) tape. 



Glass tubing of different sizes. If only a little different, build up the 

 smaller with thin rubber tubing to the size of the larger, and proceed as above; 

 if one will slip inside the other, coat i t& 2 on. of the smaller with sealing- 

 wax and slip inside the larger, which is also heated. When cold this forms 

 a very good joint, though it is not permanently tight. 



Glass tubing to stems. Proceed precisely as above described, except that, 

 if the stem is delicate, the wire must not be used, since it will cut or compress 

 the tissues; and string or a stretched rubber band must be employed. If 



2 45 



