DRAININGS. 107 



soap is pressed upon it, its original blue color will 

 be restored after washing off the substances with 

 which it has been brought into contact, — a proof 

 that in these bodies alkaline matter is contained. 

 In the freshly voided urine of a healthy man, blue 

 paper becomes red, — it is therefore acid ; red paper, 

 on the other hand, undergoes no change whatever in 

 its color. If this urine is allowed to stand in a ves- 

 sel in some warm place, and is examined every day 

 by means of the test-papers, it will be perceived that 

 after a certain time the blue paper is no longer al- 

 tered therein, but the red is ; the change which this 

 latter undergoes to blue,»is a proof that an alkaline 

 body has been generated in the urine. This alkaline 

 body is the above-mentioned ammonia, belonging to 

 the same class of bodies as wood-ashes and lime, 

 but essentially distinguished from them by the cir- 

 cumstance that it is volatile, which lime and potash 

 (the alkaline substance contained in wood-ashes) are 

 not. 



Second Experiment. — Pour, in the manner de- 

 scribed on page 39, some hartshorn into a plated 

 spoon, and hold it over the flame of a lamp, so that it 

 will become hot, whilst the vapor ascending from it 

 is allowed to mount into a large tumbler held over it : 

 after some time, the tumbler will be filled with an 

 invisible air, which possesses a very pungent odor, 

 and a strip of red test-paper, previously moistened^ 

 on being put into the apparently empty glass, will 

 in a few moments become blue. The gas escaping 



