ELECTEICITT. 



ni 



Th-ro are various kind* of fermentation, which are named 



after their pro.luots, a alcoholic, acetic, butyric fermentation*. 



It seem* that the subntance of the ferment doe* not mingle 

 with tin- pn-'l.i'-U ; but the plant or animal u propagated at 

 tii.- expense of the albumun, or other nitrogenous matter, which 

 may !> pi-.--.-n: : and, as might be anticipated, the substance of 

 the ferment i* nitron-nous matter. 



hi wliat way tho ferment duturininoa the decomposition of the 

 .-..j.ip.Min.i-- in its neighbourhood is at present a mystery. 



\olic Fermentation. When the juices of fruits, etc., which 

 i sugar are kept at a temperature of about 20" Cent, for 

 some hours, they become turhid and begin to writ, or ferment. 

 Bubbles of gas escape, which is carbonic acid. When onoe 

 this change has fairly set in, the presence of air is no longer 

 necessary. When the gas has ceased to come off, upon dis- 

 tilling tho liquor, alcohol is found to oorao over at tho commence- 

 ment of tho operation. If the liquid be examined after the 

 fermentation is complete, it is found to contain yeatt, which, 

 under the microscope, appears to be oval organised bodies, about 

 rig of an inch in diameter. These bodies cluster together, and 

 ate by budding after the manner of certain cacti. The 

 growth of this fungus is prohibited if any of tho mineral acids 

 bo present, if the solution contain more than a quarter of its 

 weight of sugar, or twenty per cent, of alcohol. The presence 

 of many of the metallic salts also arrests fermentation. There 

 seem to be two varieties of yeast oberhefe (surface yeast) and 

 a,it:'i-lu;fe (sediment yeast). The latter is the leas active of the 

 two. It appears in detached cells, which do not propagate by 

 buds, as the oberhefe, bat by spores which the larger cells 

 throw off. 



Tl\a Rising of Bread. In the making of bread, the flour 

 dough is mixed with yeast either fresh brewer's yeast, or 

 German yeast, wfyich is yeast dried by pressure a process 

 which docs not injure the vitality of the plant. Some of tho 

 starch of the flour acted upon by the yeast is converted into 

 sugar. This undergoes fermentation. The alcohol escapes into 

 the oven, and the carbonic acid being liberated from all points 

 in the dough, blows up the bread by filling it with bubbles of 

 the gas, tho walls of the hole being rendered tenacious by 

 the gluten. Bread may also be " raised " by " baking-powder," 

 or by a mixture of sodic carbonate and hydrochloric acid, the 

 result being common salt, a necessary ingredient of good bread, 

 and carbonic acid, which makes the bread spongy. 



Dr. Dauglish introduced a third method, which is used to make 

 "aerated bread." The flour is mixed in a closed iron vessel 

 with water, which is impregnated with carbonic acid gas at a 

 pressure of 100 pounds on the square inch. Tho dough is 

 drawn off into tins, and is baked in the usual way. 



New and Stale Bread. It is a popular fallacy that broad 

 becomes stale because it dries. This, however, is not true, for 

 in both cases a loaf contains as much as forty-five per cent, of 

 water. Tho soft texture of new bread seems to depend on a 

 certain molecular arrangement, which may be restored to stale 

 bread by re-heating it in the oven. To prevent too great har- 

 dening of the crust, the loaf should be steeped for a few minutes 

 in milk and water before being introduced into the oven a 

 second time. 



ELECTRICITY. V. 



SPOTTED JAB JAB WITH MOVABLE COATINGS LBYDEN PANE 



ELECTRIC PENDULUM BATTERY ELECTROMETERS 



HARRIS'S UNIT JAB EFFECTS. OF SHOCK. 



INSTEAD of coating the outside of the Leyden jar with tinfoil, 

 it may be varnished, and some metallic powder as, for instance, 

 fine brass filings sprinkled on while it is wet, a narrow band of 

 tinfoil being placed round tho top. The exterior will then be 

 illuminated as the jar is charged and discharged. To show this 

 to the greatest advantage, the knob should be bent over BO as to 

 come within striking distance of the exterior coating, and the 

 jar suspended by the loop thus formed from tho conductor, a 

 connection being made from the exterior to the ground, as 

 shown in Fig. 13. 



The piece of apparatus known as tho diamond, or spotted jar, 

 likewise affords a very interesting experiment. 



In this the glass jar, instead of being covered with a continuous 

 surface of tinfoil, has a number of diamond-shaped pieces eare 



f ully faitooMl to it in neh a way that tfadr pofeta i 

 oo another. These spangles ar uoaally ot with 

 three-fourths of an ineh long, and a hole u ponohtd oat of the 

 centre of each, so that the spark* bitwesu the poorti of tho* 

 on the interior an MOB through the afntqjaa in those ieiili. 

 The annexed sketeh will render tab mot* oleari fee atasWeart* 

 in it represent the elear glass (Fig. U). A* will be as** abort!,, 

 a plane sheet of glass may be need for this instead of ajar, and 

 it U much easier to faetoi the spangles evenly to it. OnoeiisMbla 

 care u required in placing them, bat the beauty of the expert- 

 mc-nt will repay the trouble. 



As we aaw in the hut lesson, the oppoeite noeHngi of the jar 

 act upon each other by induction; the charge, however, . 

 lodged on the rarfaoM of the flae*. and not in tbe tinfoil, a* 

 might at first be opposed. Tbe foil merely aerree to oowvey 

 the electricity, and distribute it over tbe aorfaee of the fleet. 

 An experimental proof of this can eaeily be famished. Ptoeant 

 a jar of a somewhat conical form, ae shown at (Piff. 15), an-. 

 let c be a tin or cine covering made jnst to fit it. Proeuge also 

 a cylinder of metal, D, jiuit fitting the inside of B, and bavin.- 

 a knob by which it may b- < charged fixed to it Now pot th 

 whole together, as at A, and we shall have a complete Ley dee 

 jar ; the only difference between it and those we have best 

 sidering being that the coatings are movable, instead of 

 fixed to the glass. 



This jar may now be charged in the usual way, and 

 placed upon some insulating material, such as a sheet of ghies 

 or gutta-percha. The object of this is to prevent the shock bain? 

 received when the knob is touched, for if the jar be placed on 

 table as usual, the wood, etc., will complete the circuit through 

 the person and the floor, and a violent shock will be felt ; tho 

 non-conductor, however, entirely prevents this. Having than 

 insulated tho jar, we may remove the interior cylinder by msen 

 of the rod, and, on testing it, we shall detect very little free 

 electricity in it Now carefully lift the glass by its edges oat of 

 tho outer coating ; this too, like the inner one, will be found to 

 be neutral. The proof plane, however, if applied to the inner 

 or outer side of the glass, will at onoe show the presence of 

 electricity, and on restoring the coatings the jar may be dis- 

 charged as at first If a second set of coatings be made, the. 

 jar may be placed in them, and will be found to have lost bat 

 little of its charge. 



If the glass be thick, the electricity does not all 

 the surface, but penetrates a slight distance into its . 

 This is seen by what is called the rtriduary charge. After a 

 Leyden jar has been discharged, and allowed to stand a little 

 while, a second charge much weaker than the first may be taker 

 from it, and sometimes even a third and fourth have been felt. 

 If the jar has been highly charged, and kept so for a abort time, 

 these residuary charges are stronger. The electricity appears 

 to have penetrated a little way into the glass, and therefore tbe 

 equilibrium is not completely restored at the first discharge. 

 As soon, however, as this discharge is effected, the electricity 

 gradually finds its way to the coating, thereby causing the- 

 second shock. 



It is, however, only with a thick jar that this is much noUeait 

 and such a jar does not take a very high charge ; a good jar 

 should therefore be thin, and this effect should not be seen to 

 any great degree. 



When filings are used instead of tinfoil for lining the inside 

 of a jar, these secondary shocks are much stronger; the anas*. 

 however, in this case is the want of absolute contact between 

 the particles, which prevents the electricity from passing a 

 rapicMy as it otherwise would. 



Now the effect of Induction is not affected by the shape o* 

 the interposed di-electric. and hence we may obtain similar 

 effects if we employ a sheet of glass instead of a jar. This i* 

 easily seen by taking a pane of plaits, and coating both sides oT 

 it evenly, leaving a clear margin of two or three inches all tho 

 way round. From this we shall be able to obtain a shock 

 similar to that obtained from the Leyden jar. One aide mn* 

 be held to the conductor of tho machine, and the finger placed 

 against the other, or BOOM other plan arranged to connect it 

 with the earth, and thus allow of the escape of its electricity. 

 Usually, a strip of the foil is brought from the under surface tn 

 the edge, so as to render it more convenient to ose; then tho 

 pane may bo bud down, and a wiro or chain from the conductor 

 laid upon its upper coating. If we examine the state of tbe 



