CHEMISTRY AND THE MICROSCOPE 



crystals depends on the nature of their solution. 

 A little barium sulphate should be dissolved in 

 strong sulphuric acid. Here, by the way, another 

 warning : every care should be taken in the use 

 of all acids; they should never be allowed to come 

 into contact with face, hands or clothes, nor should 

 they touch any part of the microscope. Some acids 

 give off fumes, and these should not be allowed to 

 reach the eyes or nose, and the microscope must be 

 protected from them. To continue our experiment : 

 While hot a drop of the solution of barium sulphate 

 in sulphuric acid should be transferred by means of 

 a glass rod to a slide and allowed to cool. Examina- 

 tion with the microscope will show that the barium 

 sulphate has formed small rectangular scales. With 

 the remainder of the sulphuric acid we now make a 

 saturated solution of barium sulphate, and find, on 

 repeating the method described above, that the 

 chemical has formed curious x-shaped crystals. 

 Similar experiments may be tried with calcium sul- 

 phate with the certainty of interesting results. 



Many crystals of calcium, in the form of calcium 

 oxalate, may be found in plants, and they are well 

 worth looking for. They may best be seen in sections 

 of the plants, but, if we have not mastered the art 

 of cutting sections, we may find them by teasing the 

 plant cells apart with our mounted needles. In the 

 stems of rhubarb there is the substance in bundles 

 of long needle-shaped crystals, to which the name 

 of raphides has been given. In the seed of the 

 garden poppy, just below the skin, there is a layer 



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