THE ATMOSPHERE 



13 



to find the weight of each 10 c.c. of water. Repeat the deter- 

 mination until uniform results have been obtained. Is the 

 measure correctly graduated, and are the two halves uniform ? 



Glass measures are usually graduated in such a way that each (so-called) 

 cubic centimeter is the volume of i gram of water at 15° C. (the usual 

 temperature of the laboratory), so that the water taken for the foregoing 

 experiment should be at this temperature. 



II. THE ATMOSPHERE 



Having acquired a knowledge of the methods of determining 

 the quantity of substances, the study of the 

 air may now be commenced. Firstly, has air 

 the property of weight ? 



Fit a liter flask with a cork, glass and india- 

 rubber tubes, and glass stoppers as figured, 

 and weigh it accurately upon the balance. 

 Now remove one stopper, suck out the air 

 as completely as possible, replace the stopper 

 without readmitting air, and weigh again. Has 

 the flask lost weight, and if so, what is the 

 weight of air removed ? Retain the apparatus 

 for future experiments. 



This experiment, in common with all scientific experiments, will only 

 succeed if the apparatus is perfect. Practise cork-boring on old corks 

 until true and clean bores can be made, and tube-bending on odd bits of 

 glass tubing until the bends are rounded and regular. Start boring a cork 

 from both ends so that the bores meet in the middle. To cut a glass tube 

 draw a file once only across it and snap the tube with the fingers. To bend 

 a tube use a fish-tail burner ; hold the tube near the top of the flame, 

 constantly turning it round, till the glass is soft ; then remove and bend. 

 Before pushing a glass tube through a cork, or fitting it with rubber tubing, 

 always round off the sharp edges by just melting the glass in the Bunsen 



