12 INTRODUCTION. 



upon until the foreign matter has been removed by the agents 

 previously spoken of (see 26). 



This reagent, known as Schweizer's, 1 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 

 libres used in the arts. 



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

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

 is kept in a concentrated solution for some days, 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 by Unverdorben. 2 



57. Ciij>nc sulphate in saturated aqueous solution is used 

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

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

 two or three times, will answer for all ordinary cases. 



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



59. Ferric chloride in aqueous solution was formerly recom- 

 mended ns a test for the tannins; 3 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. Only the purest glycerin should 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 the Ilanstein 

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

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



* o 



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

 of the glycerin. 3. In the examination of protein granules 

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

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

 for iodine (see 31). 



61. Hydrochloric acid. Pure concentrated acid is one of the 

 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 



1 Schweizer: Vierteljahrsschrift natur. Ges., Zurich, 1857. 



2 Behrens: Hilfsbuch, p. 377. 



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



