142 Laboratory Arts 



X. BURETTE STOPPER GREASE. 



The most suitable grease for this purpose is made by melting 

 together equal parts of resin cerate and vaseline. The mixture 

 is only applied to a perfectly dry stopper, and a smear is all 

 that is required. It is placed on either side the bore, and the 

 stopper slipped into the dry barrel of the tap, pushed home, and 

 rotated until the whole becomes transparent. If this does not 

 happen, remove the stopper and add a little more grease. The 

 usual fault, however, is that of using too much grease. 



XI. POLEFINDING PAPER. 



One gram of phenol phthalein is dissolved in absolute 

 alcohol, poured into 100 c.c. distilled water, containing 

 10 grams pure potassium chloride. 



Filter paper strips are then soaked in the liquid and hung 

 up to dry. When two electrical leads are placed close 

 together upon a piece of moistened prepared paper, the 

 negative pole shows a red stain. 



XII. LITMUS SOLUTION. 



Litmus solution is spoiled by heating. It should be made 

 by extracting the solid litmus with cold distilled water, and it 

 should be preserved in bottles, which allow access to the air, 

 otherwise the colour will disappear. 



XIII. COLOURED LIQUID FOR EXPERIMENTS IN 

 HYDROSTATICS, ETC. 



The best substance for this purpose is fluorescin. A 

 i per cent, solution of the solid in spt. vini. rect. is kept in 

 stock, and a few drops added to the bulk of water. One drop 

 per litre is sufficient to produce an easily visible colour, and 

 the apparatus may be washed clean without trouble afterwards. 

 It does not stain or cause any trouble, and is easily visible, 

 even in very dilute solution. 



