12 INTRODUCTION. 



upon until the foreign matter has been removed by the agenta 

 previouslj- spoken of (see 26). 



This reagent, known as Schweizer's,^ possesses its chief in- 

 terest from the fact that it is the only liquid known in which 

 cellulose appears to dissolve without essential change of compo- 

 sition. It has a limited application in the discrimination of 

 fibres used in the arts. 



56. Gupric acetate in aqueous solution is used as a preparatory 

 liquid for the examination of resins. The part to be examined 

 js liept in a concentrated solution for some dajs, and sections 

 are then made from it. If certain resins are present, they will 

 appear of a green color. The above is Franchimont's test based 

 on a reaction discovered b} Unverdorben.^ 



67. Ciqoric sulphate in saturated aqueous solution is used 

 for the detection of certain carbohydrates (see 184) and albumi- 

 noidal matters (sec 124). Commercial blue vitriol, recrystallized 

 two or three times, will answer for all ordinarj- cases. 



58. Ether is used as a solvent for fats, etc. 



59. Ferric chloride in aqueous solution was formerly recom- 

 mended as a test for the tannins;^ the tannin of oak-bark be- 

 coming bluish-black ; that in the leaves of the sumach, greenish- 

 black. But the distinctions are not constant. Ferric acetate 

 and sulphate are now more generally' used than the chloride as 

 a test, and are better. 



60. Glycerin. Onl^- the purest glycerin sliould ever be em- 

 ployed in microscopic examinations. The following are among 

 the most important of its many applications: 1. In clearing 

 specimens. It is used not only as an adjuvant in tlie Hanstein 

 and other methods of clearing, but, in man3- cases, it serves well 

 without any other reagent. 2. To cause withdrawal of water 

 from fresh cells, the degree of effect depending on the strength 

 of the glj'ceriu. 3. In the examination of protein grannies 

 (see 175). 4. As a test for inulin; this substance separates 

 sooner or later in the form of sphajrocrystals. 5. As a solvent 

 for iodine (see 31). 



61 . Hydrochloric acid. Pure concentrated add is one of tlie 

 most satisfactory agents for the maceration of woody tissues. 

 When dilute, it serves for the discrimination between carbonates 

 and oxalates, the former dissolving with effervescence, the latter 



- Sohweizer: Vierteljahraschrift natur. Ges., Ziuich, 1857. 



' BehrensrHilfsbuch, p. 377. 



" Watts's edition of Fownes's Chem., p. 672. 



