38 



GEADUATION OF LIQUID MEASURES) 



the tube from the jet of the washing-bottle until equilibrium is 

 restored. The height of the water in the tube is marked by a 

 pencil line on the paper. In the smaller tube quantities of one, 

 two, three, etc., up to ten grammes, are successively weighed out, 

 in the larger tube first 5 grammes, then 10, etc., up to 50 grammes. 

 The surface of water in a glass vessel is not quite level, but 

 forms a concave * meniscus.' To avoid errors the same boundary of 

 the meniscus should always be read off ; it is better to take the 

 lower, a in fig. 38, because it is best defined. It is also necessary to 

 hold the measure always perpendicularly, not only while marking 

 off the divisions, but also whenever any liquid is measured by the 

 graduated scale. When the larger divisions have been determined, 

 they may be divided by a pair of compasses into subdivisions ; the 

 lines are then neatly drawn with Indian ink, and the paper, after 

 the ink has become dry, washed over with a thin solution of gum 

 arabic, and finally, when again quite dry, with varnish. The 

 varnish protects the paper from moisture, and the gum prevents 

 the varnish from penetrating the paper, and thus rendering the 

 divisions unsightly. The lowest division in each graduated tube 



10 



15 



20 



Fio. 38 (real size). 



FIG. 39 (real size). 



cannot be subdivided into equal parts on account of the rounded 

 shape of that part of the vessel. Fig. 39 shows the arrangement of 

 the whole graduation. 



Divisions which are etched on the glass are neater and more 

 durable than those drawn on paper. Such graduated measures 

 are not very expensive, and may be purchased, while larger 

 measures for liquids require no great accuracy, and may easily be 

 made by pouring into a glass vessel with stout sides gradually 

 50, 100, 150, etc., up to 500 r of water, and marking the height of 

 the liquid each time by a scratch with the three-cornered file. 



Equal volumes of different bodies have often very 





