WITH THE MICROSCOPE. 2O/ 



303. >itratc of silver. A solution of nitrate of silver is pre- 

 pared by dissolving one hundred and twenty grains of the 

 crystallised nitrate in two ounces of distilled water, and filtering 

 if necessary. Nitrate of silver is employed as a test for chlorides 

 and phosphates. The white precipitate of chloride of silver is 

 soluble in ammonia, but insoluble in nitric acid. The yellow pre- 

 cipitate of tribasic phosphate of silver is soluble in excess of 

 ammonia, as well as in excess of nitric acid. 



304. Oxaiate of Ammonia. Some crystals may be dissolved in 

 distilled water, and, after allowing time for the solution to become 

 saturated, it may be filtered. Oxaiate of ammonia is used as a test 

 for salts of lime. Oxaiate of lime is insoluble in alkalies and in 

 acetic acid, but soluble in the strong mineral acids. In testing an 

 insoluble deposit for lime, it may be dissolved in nitric acid and 

 excess of ammonia added ; the flocculent precipitate is readily 

 dissolved by excess of acetic acid, and to this solution the oxalate 

 of ammonia may be added. The precipitation of oxalate of lime 

 is favoured by the application of heat. Many deposits of phosphate 

 are with great difficulty soluble in acetic acid, hence the necessity of 

 first adding nitric acid, as above directed. 



305. iodine Solutions. An aqueous solution is easily prepared, 

 by dissolving a few grains of iodine in some distilled water, until it 

 acquires a brownish-yellow colour. A solution of iodine is sometimes 

 useful for colouring certain animal and vegetable textures, which are 

 so transparent as to be scarcely distinguishable upon microscopical 

 examination. In the examination of many such structures, great 

 assistance will be obtained from the use of coloured solutions ; for 

 delicate textures, like the cell-wall and basement membrane, &c., 

 can be far better distinguished when a faint tint is communicated 

 to them, than when perfectly colourless. When a membrane 

 is to be made more distinct, it may be immersed in a little Prus- 

 sian blue fluid, p. 93, the minute particles of which adhere to it, 

 and enable us to trace its outline clearly. A weak solution of 

 magenta answers the same purpose. 



Iodine is principally employed as a test for starch which is 

 rendered blue by an aqueous solution, even when very dilute. 

 Albuminous matters and tissues are coloured yellow by iodine, and 

 vegetable cellulose also receives a brownish-yellow tinge. The 

 addition of sulphuric acid (one part of the strong acid, two parts of 

 water) to albuminous matter stained with iodine, causes no change, 

 but cellulose under the same circumstances becomes blue. In cases 

 where substances allied to starch and cellulose (amyloid matters) 

 are found associated with the albuminous matters, a purple, bluish, 



