and Observations on the component Parts of Membrane. 377 



the experiments made on bladder, and some other membranes. 

 It may therefore suffice here to observe, that all these bodies 

 afforded more or less gelatin ; that, when this was separated, the 

 remaining substance ceased to be tough, or elastic, and was easily 

 torn, like wetted paper ; and that, when dry, the sponges, and 

 such membranes as bladder and cuticle, became very brittle, and 

 were shrivelled and curled up, like withered leaves of plants. 



But, before I speak of the nature of the substance which thus 

 remained, it will be proper, concisely to notice the effects of 

 acids on the bodies which afford gelatin ; and, as the most re- 

 markable effects were produced by nitric acid, I shall to that 

 confine the present observations. 



The specific gravity of the nitric acid which I employed in 

 the whole of my experiments, was 1,38 ; and this acid was diluted 

 with 2, 3, or 4 measures of distilled water, according to the 

 quality of the substance under examination, and the intended 

 time of immersion. But, as an acid too powerful would have 

 frustrated my intentions, I commonly added the aciJ, by de- 

 grees, and at long intervals, to the water in which the substance 

 was immersed ; during which time, if any nitrous gas was dis- 

 charged, more water was added, as this gas was a certain sign 

 that the acid was not sufficiently diluted. 



Substances like the Corallina officinalis, which contain a large 

 quantity of animal mucilage, or of the least viscid jelly, soon 

 impart it to boiling water. 



In like manner, when such substances were steeped in nitric 

 acid diluted with about three measures of water, the mucilage 

 was in a few hours completely dissolved, while the membrana- 

 ceous part remained untouched. 



Pure isinglass dissolved in the diluted nitric acid, formed a 



3C 2 



