The Rev. E. Craig's Remarks on Microscopic Chemistry. 11 



pressure of the atmosphere : this suggested a furtlier inspec- 

 tion into the form and character of the smallest discoverable 

 particles of any pure chemical precipitates, many of which I 

 found to be circular in the form of their molecular particles. 

 From this the step was made naturally and almost necessarily 

 to the observation of chemical action. The plan adopted for 

 placing very small particles of matter in a floating state of thin 

 film under the microscope, presented also an ample means 

 for submitting to equally accurate scrutiny equally small por- 

 tions of substances in a state of reaction : a few sentences will 

 detail the plan. The phsenomena may in a tew cases be de- 

 scribed, and then the interminable field of such inquiry will 

 be fully open to any one who delights in the novelty of new 

 modes of scientific research. The veriest tyro and the most 

 advanced chemist will be alike interested in the wonders that 

 open to his view. 



The microscope which I use was made by Chevallier of 

 Paris, and is peculiarly well adapted for the purpose. The 

 port-object is a broad brass tablet perforated in the middle to 

 receive reflected light from below, and fitted also with a 

 powerful convex lens to throw light from above. It is steady 

 and firm, which is very desirable. The whole additional ap- 

 paratus necessary is a number of small plates of thin and 

 very flat glass, filed at the edges to prevent them from cutting 

 the finger, and a io-yf glass rods with small rounded ends 

 for taking up a drop of liquid. The glasses should be free 

 from flaws and fitted to lie closely with even pressure upon 

 one another. 



When I wish to examine the action of two substances I lay 

 a plate of glass on the port-object, and put on it a very mi- 

 nute portion of one substance ; I adjust this to the tbcus of 

 the lens in use, and ascertain the form and character of the 

 substance in a quiescent state. I then lengthen the distance 

 of the object-glass from the object a little to prepare for the 

 subsequent observation ; for I find that in the use of high- 

 powered lenses the introduction of a second plate of glass al- 

 ters the focus : and this must be provided for, as one instant 

 lost, after the two chemical agents are in contact, is of im- 

 portance. 1 then draw the glass a little aside, and holding in 

 my hand another plate of glass, I put on it the other sub- 

 stance, say a drop of acid. I spread both to an equal extent 

 on their respective glasses, and then quietly and carefully 

 turning down the one upon the other, I push them gently 

 forward, by the application of a fine point to the edge of the 

 lower glass only, to their proper place on the port-object. 

 The upper glass should never be touched after it is turned 



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