CHEMISTRY AND THE MICROSCOPE 



merits we have described for themselves can obtain 

 all the necessary substances, except the poisons, at 

 any chemists and the quantities required will only 

 be the smallest that can be obtained, in fact any 

 reasonable-minded chemist would probably let a 

 microscopist whom he knew have a few grains of 

 a large number of chemical substances, suitable for 

 this work, at the outlay of a few pence. The 

 chlorides of gold and platinum we fear no one will 

 give away. 



All the experiments we have described thus far 

 have necessitated the use of what are called in- 

 organic substances, they may be described in every 

 day language as substances derived from the in- 

 animate world. There are many equally interest- 

 ing tests which may be carried out with animal 

 and vegetable products. 



Formic acid is the substance which renders the 

 sting of ants so painful ; it may, however, be pre 

 pared artificially and if a little, dissolved in water, 

 is mixed with a solution of silver nitrate we shall 

 obtain flat plate like crystals also some resembling 

 fine fibres. 



Probably the most curious of the easily obtaine 

 crystals from vegetable products, may be made 

 from citric acid which occurs in lemons. If a little 

 of the acid be mixed with a solution of caustic soda 

 and boiled with calcium chloride, a drop of the 

 liquid after boiling placed on a slide will give 

 crystals readily. When viewed from above they 

 are an elongated oval shape, described by some| 



258 



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