THE CONTROL OF THE FACTORY. 



Steel knife edges are unsuited for a damp tropical climate, and balances 

 with agate fittings, though more expensive, are more satisfactory. The routine 

 of weighing out, say, an exact quantity of sugar is as follows : 



1. See that the balance is in equilibrium, when the vessel destined 

 to contain the sugar and the counterpoise supplied by the makers are in place, 

 and if not, adjust with small pieces of tin foil. 



2. The vessel to contain the sugar being on the left-hand pan, place on 

 the right-hand pan the weight which it is wished to obtain, and approximately 

 the desired quantity of sugar in the containing vessel, then adjust the quantity 

 of sugar until balance is obtained. Never weigh any material directly on the 

 pans, and never place or remove anything from the pans when the beam is 

 free to move; the final adjustment should be made with the sliding door 

 closed. 



When weighing out large-grained sugars, an exact 

 balance is difficult to obtain; in this case a little of the 

 sample can be crushed and the final adjustment made with 

 the powdered sugar. 



The Burette. A burette (Fig. 27 Ij) is a narrow cylin- 

 drical graduated glass tube provided with a cock at one end ; 

 by opening the cock any desired volume of liquid can be run 

 out. For laboratory purposes the graduation is made in one- 

 tenth of a cubic centimetre. Burettes are sent out by reliable 

 dealers very accurately calibrated and no appreciable error 

 need be looked for. The method of use is as follows : the FlG< 274 * 



burette is rinsed out with the liquid to be used, filled and placed in a vertical 

 position in the holder ; the level of the contained liquid is adjusted by opening 

 the cock until it corresponds exactly with some mark, say, 10*3; after a test 

 has been made the level of the liquid is again noted, say, 27*6 c.c., showing 

 that 17'3 c.c. have been used. 



After use, if the burette is to be put away for any long period, 

 the cock should be wiped dry and smeared with vaseline ; if allowed 

 to dry with the liquid remaining, the cock will probably become 

 fixed, and efforts to remove it will possibly lead to fracture of the 

 instrument. 



The Pipette. A pipette, Fig. 275, is a special form of burette 

 designed to deliver one definite quantity of liquid. It consists of a 

 narrow piece of glass tubing in the centre of which is blown a bulb ; 

 on the upper part of the stem is a mark. The pipette is filled by 

 suction, the lower end being immersed below the level of the liquid 

 and the liquid aspirated up into the burette until a little above the level of 

 the graduation mark ; the filled burette is then smartly removed from the 



513 



FIG. 275. 



33 



