606 SUMMARY OF CUERENT RESEARCHES RELATING TO 



analysis and meclianical test, which have thus far, to some extent, run 

 in parallel lines. When, between the report of analysis and the 

 fracture of the broken test-piece, we can place a polished longitudinal 

 or cross-section of the material, its internal structure developed by 

 acid and admitting of careful microscopical study, we are furnished 

 with the missing link in the chain of evidence required for a correct 

 conclusion as to the nature of the material under investigation. 



Microchemical Reaction Methods.* — A. Tschirch describes the 

 great advantages of the Microscope in technical chemistry, especially 

 in the examination of foods, and expresses regret that many chemists 

 consider their laboratories complete without such an instrument : he 

 enumerates many examples of its usefulness, such as starches, textile 

 materials, &c. ; even in the domain of pure chemistry, its application 

 is necessary in the htematin reaction for the detection of blood- 

 stains, the composition of urinary deposits, the search for strychnine, 

 atropine, &c. 



These advantages led to its more extensive employment in pure 

 chemistry, and the name of microchemistry was given to it by 

 Dobereiner. The author thinks that microchemistry must always be 

 distinguished by a series of colour reactions, that in the same manner 

 as the changes of colour, &c., in experiments on the large scale are 

 examined in the test-tube, so must they be similarly observed on the 

 slide of the Microscope. The actual process is simple ; the objects 

 to be examined must be either in thin sections, fine powder, or as 

 fibres ; a drop of the reagent is placed on a slide and allowed to flow 

 slowly towards the object, the operator observing through the instru- 

 ment: many physical as well as chemical changes may be thus 

 detected ; expansion or contraction, refractive changes, commencement 

 of coloration, evolution of gas bubbles, solution, &c. The iodine 

 starch reaction of Stromeyer was the first to be employed with the 

 Microscope ; from it is learned the topography and division of starch 

 in plants, the way it is stored up, and the prucess of its conversion ; 

 this reaction has also taught the difference between pure cellulose and 

 woody fibre, and the nature of intercellular substance. The reactions 

 with zinc chloride and iodine, and with sulphuric acid and iodine, are 

 also striking instances of the value of microchemistry, affording an 

 easy method of distinguishing vegetable from animal fibres, the first 

 colouring pure cellulose violet, and the second dissolving it with an 

 intensely blue colour, the lignin incrusting the fibres having been 

 previously moved by maceration in nitric acid, alkalis, or Schultze's 

 maceration fiuid. Thus sulphiu'ic acid and iodine stain cork dark 

 yellow, thereby affording a trustworthy test for all membranes or 

 sections containing suberin. The solubility of pure cellulose in 

 " cuoxam," discovered by Schweitzer, is also credited to micro- 

 chemistry : the reagent may be prepared by digesting copper turnings 

 in concentrated ammonia, or by decomposing a concentrated solution 

 of copper sulphate with ammonia until the precipitated hydroxide is 

 redissolved. 



* Arch. Pharm., xx. (1882) pp, 801-12. See Journ. Cheiii. Soc— Abstr., 

 xhii. (1882) pp. 37G-8. 



