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 

 fibres used in the arts. 



56. Cupric 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 Franchiniont's test based 

 on a reaction discovered by Unverdorben. 2 



57. Cupric sulphate in saturated aqueous solution is used 

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

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

 two or three times, will answer for all ordinary 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; 8 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 Hanstein 

 and other methods of clearing, but, in man}* 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 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 sphserocrystals. 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 



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



2 Behrens:Hilfsbuch, ].. 377. 



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



