WEIGHTS. 35 



A balance for the following experiments should be capable of 

 carrying at least one kilogramme, and of indicating a difference 

 of th of a gramme when the weights in both scales are com- 

 paratively small. Such a balance may be bought for a small sum. 

 A common grocer's balance is also suitable for many purposes, but 

 is usually not very delicate. The weights required range from Os r 'l 

 to l k r . In any case a set of the following weights made of brass 

 should be purchased, viz. : 



20s r ; 20s r ; 10s r ; 5 r ; 2 r ; 2s r ; le r ; 0& r '5 ; 0* r '2 ; r '2; r 'l ; 

 while the larger weights of 00g r , 200 r , 200s r , 100s r , and 50^ may 

 either be purchased or made of lead. Procure for this purpose a 

 cylindrical piece of wood, 3 cm thick and 5 cm long, from the turner, 

 or cut one with a knife. Wrap a strip of strong packing paper, 

 from 6 to 12 cm broad, and 40 or 50 cm long, round the cylinder, 

 so that it projects at one end, and tie it firmly with thread. A 

 paper mould is thus obtained for pouring in the lead. Each time 

 a little more metal must be taken than the weight to be formed, 

 as a little is lost in the melting, which may be performed over a 

 common fireplace in a capacious ladle of sheet-iron with a wooden 

 handle. The film over the molten lead should be removed with a 

 splinter of wood before pouring the metal into the mould ; the 

 wooden cylinder should also be heated near a fireplace as strongly 

 as possible without burning it, for if the wood is not perfectly dry 

 bubbles of vapour are produced, and passing into the liquid . metal 

 render it spongy. The paper must be renewed for each weight 

 which is to be produced. The pieces are corrected to the exact 

 weight which they are to represent by careful cutting, and finally 

 cautious scraping. If you have no other weights than the above- 

 mentioned small set, make first a 50-gramme piece by placing into 

 one scale 20 +20 +10 4-5 + 2 + 2+1 = 60s r , and thus 

 weighing out 60s r of lead. The cast piece is then corrected to 50s r 

 (20 + 20 + 10), and with the help of this new weight and the 

 others now make a 100s r weight, and so on. All these weights 

 have a diameter of 3 em , they are easily distinguished by their 

 different heights, and therefore require no particular marking. 

 The 500 r piece will have a height of about 7 cm , that of 50* r of about 

 cm . The lead is generally bought in rather large pieces, but in 

 order to weigh out any required quantity it is convenient to granu- 

 late it, by pouring it in a molten state into water, in the manner 

 previously described in the case of zinc. 



Having procured a balance and the necessary weights, the next 

 step is to provide yourself with a number of liquid measures, which 

 are frequently required, and may all be prepared by weighing out 



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