374 HISTORY OF SCIENCE. 



However disputed have been the claims of various chemists to the 

 honour of having first suggested and proved by synthetical experiments 

 that water was composed of inflammable air and vital air, it is admitted 

 that Lavoisier is entitled to the priority in having analytically demon- 

 strated this great truth. First, let us see how he showed that metallic 

 " calxes" were combinations of metals with oxygen; that is, according 

 to his nomenclature, they were oxides. Oxygen, he says, has a stronger 

 affinity for metals that are heated to a certain degree than for caloric 

 (page 310). In consequence of this all metallic bodies, excepting 

 gold, silver, and platinum, have the property of decomposing oxygen 

 gas by attracting its base from the caloric with which it was combined. 

 Lavoisier showed experimentally that iron wire burns with splendour 

 to the last particle in oxygen gas. He found that the metal is con- 

 verted into what the old chemists called martial etkiops, and that every 

 100 grains of iron burnt yielded 135 grains of this substance (which 

 is, in fact, oxide of iron), and that the weight of the oxygen which had 

 disappeared was equal to that which the iron had gained. In such 

 experiments it is in general necessary to apply heat to start the com- 

 bustion ; for instance, the iron wire in the above experiment was set 

 on fire by a piece of ignited tinder. Lavoisier had a theory about this, 

 namely, that the heat is required to separate the particles of the metals 

 from each other, so as to overcome in some degree at least their mutual 

 attractions. Metals by uniting with oxygen lose their lustre, and be- 

 come changed into dull pulverulent matters, which the older chemists 

 (by false analogy with the effects of heating limestone) called calxes. 

 Now, when Lavoisier had established the fact that iron directly unites 

 with oxygen, producing an " oxide " possessed of certain properties, 

 the following experiments, which he performed with the apparatus de- 

 picted in Fig. 176, were perfectly conclusive. G"G is a glass tube 

 passing through the furnace F. The tube G"G, which was made of 

 difficultly fusible glass, and was coated externally with a lute, to defend 

 it from the too powerful action of the fire, had a slight inclination from 

 G towards G", and was connected at G with the retort i, containing a 

 weighed quantity of pure distilled water. At G' the glass tube was 

 luted to the upper end of a worm-tube, and surrounded by cold water 

 in the vessel H. The lower end of the worm-tube led into the double- 

 necked bottle j, from which a tube passed under the bell jar K, stand- 

 ing in the pneumatic trough L. The experiments proceeded thus : 

 first the fire was lighted in the furnace F, and when the tube G"G had 

 become red hot, heat was applied to the retort i, so as to boil away 

 all the water. The steam was condensed in the refrigerating vessel H r 

 and the weight of water found in j was equal to that which had passed 

 from the retort. So far. then, the operation was a simple distillation, 

 and the result proved that the water had undergone no change by 

 passing though the red-hot glass tube G"G. The apparatus was then 

 rearranged for a second experiment exactly as before, except that 274 



