APPLICATION OF CHEMICAL EE-AGENTS. 197 



by the ■warmth of the hand applied to the bottle, which causes an 

 expansion of the air it may contain : the perforated stopper, when 

 not in use, is covered by a cap which fits closely around the neck 

 of the bottle. * Or the tubular stopper may be shaped like that of 

 the bottle represented in Fig. 102, the lower end of the tube being 

 drawn to a fine point, so that the desired quantity of the test- 

 liquid, and no more, may be made to flow from it by pressing the 

 elastic cap of the funnel. Another arrangement consists in the 

 elongation of the stopper, which is drawn to a fusiform point, so 

 as to serve as the test-rod for its own bottle, + thereby enabling either 

 a mere trace or several ordinary drops of the re-agent to be applied 

 at once ; for the elongated stopper will take up a considerable 

 quantity, a larger or smaller proportion of which (as desired) may 

 be left behind, by bringing the lower part of the stopper into con- 

 tact with the inside of the neck of the bottle as it is being with- 

 drawn. The Author is disposed, however, from his own experience, 

 to recommend the small Syringe formerly described (§ 101), with 

 its nozzle drawn out to a point, as the most convenient instrument 

 for applying minute quantities of Test-liquids to Microscopic objects. 

 "Whichever plan is made use of, great care should be taken to 

 avoid canying away from the slide to which the test-liquid is 

 applied any loose particles which may be upon it, and which may 

 be thus transferred to some other object, to the great perplexity of 

 the Microscopist. It is better, indeed, not to deposit the drop of 

 test-liquid on the slide in immediate contact with the substance to 

 which it is to be applied ; but to bring the two into contact after 

 the test-bottle, stopper, or syringe has been withdrawn. 



144. The following are the Test-Liquids most frequently 

 needed : — 



1. Solution of Iodine in water (1 gr. of iodine, 3 grs. of iodide 

 of potassium, 1 oz. of distilled water) turns Starch blue and 

 Cellulose brown ; it also gives an intense brown to Albuminous 

 substances. 



2. Dilute Sulphuric Acid (one of acid to two or three parts of 

 water), gives to Cellulose that has been previously dyed with iodine 

 a blue or purple hue ; also, when mixed with a solution of sugar, 

 it gives a rose-red hue, more or less deep, with Nitrogenous sub- 

 stances and with bile (Pettenkofer's test). 



3. Solution of Chloride of Zinc, Iodine, and Iodide of Potassium, 

 made in the following way : — Zinc is dissolved in hydrochloric acid, 

 and the solution is permitted to evaporate, in contact with metallic 

 zinc, until it attains the thickness of a syrup ; this syrup is then 

 saturated with iodide of potassium, and iodine is last added. This 

 solution (which is known as Schultz's test) serves, like the preceding, 

 to detect the presence of Cellulose, and has the advantage over 



* A set of 12 test-bottles on this plan is supplied by Mr. Highley. 

 + Bottles of this pattern, which was devised by Dr. Griffith, are sold 

 by Mr. Ferguson, of Giltspur-street. 



