CHEMISTRY AND THE MICROSCOPE 



chloride of tin, known as stannous chloride, in an 

 evil smelling liquid called chlorine water. If now 

 we watch our drop of gold solution under the micro- 

 scope, and while watching mix with it a drop of 

 stannous chloride solution, a strikingly beautiful 

 purple colouration is produced — this purple has been 

 named the purple of Cassius. 



If we desire further experiments in the testing 

 of common substances, and incidentally in the pro- 

 duction of beautiful crystals, we might do worse 

 than try the effect of adding a solution of platinum 

 chloride to any solution containing a compound of 

 potassium. Charmingly beautiful crystals will 

 result. 



The experiments we have described as well as 

 hundreds of others are used by analysists every 

 day in the testing of various substances. We have 

 started in every case by knowing what our solutions 

 contain; the duty of the analyst is to discover what 

 he has before him. Given an unlimited quantity of 

 a substance for testing purposes it is not always 

 easy to determine its composition. With very small 

 quantities, perhaps less than a tea-spoon full in all, 

 the difficulties of the analyst are increased ten- 

 fold and without the assistance of the microscope his 

 efforts would be unavailing, he deals in drops and 

 every drop is precious. Sad to relate this form of 

 testing, known to science as micro-chemical analysis 

 has been practised to a far greater extent on the 

 continent than in this country. 



Those of our readers who wish to try the experi- 

 257 B 



