516 REPORTS ON THE STATE OF SCIENCE, ETC. 



Where does the fire come from? It seems to have its origin in the act of 

 association, does it not? What becomes of the fire or heat PJ'oduced on 

 associating phosphorus with Fire air? It escapes, does it not? Ihe llask m 

 which the phosphorus is burnt becomes unbearably hot m places but soon cools— 

 the heat is soon lost : does it, the heat that is lost, weigh anything ? Try ! _ 

 You have thus made the discovery— the wonderful discovery— that fire is 

 weightless— something unsubstantial, unmaterial— but consider what strange 

 changes attend its production : the metal iron and Fire gas give rise to the 

 earth-like rust ; the phosphorus and the Fire air to phosphorus snow ; the vanouB 

 ordinary combustibles, whether gaseous, liquid or solid, seem to afford vvater 

 and something which has escaped our notice hitherto, which probably therefore is an 

 air-like or gaseous substance : but if so, it must be quite soluble in water, must it 

 not, as nearly one-fifth of the air disappears when the various substances are burnt 

 in it ? Stay, now, do you know that all substances burn at the expense of one and 

 the same constituent of air ? Will it not be well to try whether, in all cases, the 

 inactive four-fifths left after exposing iron or phosphorus in air be inactive also towards 

 all ordinary combustibles ? In this work, nothing must be taken for granted. Also 

 do you know that when iron and phosphorus ' rust ' in air heat is produced as when 

 phosphorus actually burns in air ? Is heat given out when the phosphorus is merely 

 exposed in air ? Make the experiment in a really warm room, usmg a thin rod of 

 phosphorus lashed to a wooden rod. 



You thus obtain evidence that even when the Fire air is absorbed slowly, 

 heat is produced, and you can believe that whether the phosphorus burn visibly or 

 not is merely a question of the rate at which the change takes place — whether the 

 heat have time to get away or not. 



You may ask : Is the rusting of iron a case of slow burning ? The reply is — 

 Can iron burn? How were fires lighted before matches were known— how 

 were guns fired before percussion cape were invented? With the aid of a 

 flint and steel. Try the effect of striking pieces of flint and of iron together. 

 If you can find a smithy, watch the blacksmith at work at his forge ; still 

 better, go to a steelworks where iron is rolled into bars and plates. Examine 

 a new horseshoe and contrast its surface with that of one which has been in 

 use. Examine the ground near the smith's anvil. Heat a piece of bright 

 iron to redness for some time and notice the effect ; then prepare some coarse 

 iron filings and heat them in a muffle furnace on a clay support, weighing them 

 before and after heating. 



Having thus ascertained that iron can be burnt, you will be prepared to 

 regard rusting also as a case of slow burning — whether it rust slowly or burn 

 rapidly, it equally combines with Fire air and becomes converted into a 

 pulverulent, earthy substance : a red earth in the one case, a black earth 

 in the other. 



You will perhaps ask — do other metals burn ? Do other metals give earths 

 when burnt? Metals are so commonly used in household practice that it will 

 be well to know something about them. Copper vessels are commonly used — 

 does copper combine with Fire air and burn? Try! Does lead, does zinc, does 

 tin ? You can easily try. Magnesium, in the form of ribbon, burns very 

 easily — study the change carefully. Try also if silver can be burnt. 



Having previously contrasted iron with iron rust by determining their 

 densities, it will be well in the case of other metals to contrast each of the 

 products with the metal from which it is formed and to draw up a tabular 

 statement of the results arrived at. It will be well, instead of making all the 

 substances, to inquire if you cannot obtain the various burnt metals and at 

 the same time to collect information as to the use that is made of them and 

 of their market value in comparison with that of the metals. At the same 

 time, it will be well to inquire how the metals are made. 



Such a comparison affords most instructive results — in every case, the metal 

 affords an earthy product : some of the earths are relatively light, others 

 heavy — some are coloured, others colourless; how do they behave towards 

 water — have they any taste ? 



All this time, the snow formed on burning phosphorus — which is certainly 

 not at all like a metal — has been left out of consideration : it should therefore 



