APPENDIX A. 309 



be provided with a supply of copper sulphate and of 10% 

 sulphuric acid in large siphon bottles similar to the one 

 suggested for normal salt solution (Fig. 53), except that 

 instead of the short tube for equalizing pressure one may 

 insert a filter through which at the end of the laboratory 

 period the student may return the liquids. 



The accumulation of zinc sulphate in the acid makes 

 the renewal of the acid necessary from time to time. The 

 deposit of metallic copper upon the copper plate reduces 

 the copper sulphate solution in strength. It may be kept 

 replenished by an excess of crystals of that salt in the large 

 supply jar. A very practical method of amalgamating the 

 zinc plates is to have a jar containing 10% sulphuric acid 

 with mercury in the bottom; as the plate is immersed the 

 acid attacks it and cleans it so that the mercury readily 

 clings to it and may be rubbed over the surface with a 

 cloth. Another method, which is preferred by some, is as 

 follows: Dissolve 75 gms. of mercury in a mixture of 150 

 c. c. strong nitric acid and 300 c.c. strong hydrochloric 

 acid. Add to the solution 450 c.c. of strong hydrochloric 

 acid. Keep this amalgamating solution in a ground glass 

 stoppered jar. To amalgamate a zinc plate one need only 

 dip it for a few moments into the solution, remove it, rinse 

 under the spigot and rub with a cloth. 



At the end of each laboratory period the cells should 

 be emptied, the zinc plates rinsed and drained, and the 

 porous cups left in a tray of running water, or at least in 

 a considerable excess of water. 



5. To curarize a frog. 



In experiments on the irritability of muscle tissue it is 

 necessary to, in some way, suspend the activity of the 

 irritable nerve fibers which are supplied to every muscle. 

 In certain other experiments it may be advisable to thus 



