1856.] the Chemical Type : Ammonia. 276 



tion of inquirers. It was only much later : — in fact, at a comparatively 

 recent epoch, that the vegetable and the animal world were drawn 

 into the circle of chemical observation. The progress made in the 

 study of vegetable and animal substances was based, in the com- 

 mencement at least, entirely and exclusively upon the knowledge 

 which chemists possessed of mineral bodies. The experience, the 

 ideas, gained in the examination of mineral substances, reflected 

 themselves, if I may use this expression, in whatever views were 

 brought forward regarding the nature of vegetable and animal 

 compounds. Organic Chemistry was but a reproduction, in another 

 form, of Mineral, or Inorganic Chemistry. 



This aspect, however, of the relative position of the two depart- 

 ments of the science is rapidly changing. The amount of material 

 accumulated by the indomitable perseverance of so many cultivators 

 of Organic Chemistry, (a chaotic and almost inaccessible labyrinth, 

 but a few years ago,j is rapidly assuming shape and order. The 

 study of organic bodies has led to the observation of general laws, 

 which could have never been discovered by the examination of 

 mineral substances alone, but which begin to react in a most 

 powerful manner upon our ideas regarding the constitution of these 

 very mineral substances. The progress of our knowledge of 

 organic bodies has opened new points of view, from which the con- 

 stitution of mineral substances appears to us in a brighter light, in 

 a simpler and more intelligible form. In one word. Organic 

 Chemistry is beginning to repay, and I venture to say, with in- 

 terest, the debt of gratitude which it owes to her elder sister, 

 Mineral Chemistry. 



It is my task, this evening, to bring under your notice some 

 especial examples in elucidation of the idea which I have 

 endeavoured to delineate to you. Illustrations of this kind might 

 be taken from widely different departments of the science. In 

 consequence of special studies and predilections of my own, I have 

 selected as material of illustration a class of substances of which 

 the well-known compound Ammonia is the type. 



The four elements — Nitrogen, Phosphorus, Antimony, and 

 Arsenic, although essentially differing in many of their physical 

 properties, exhibit nevertheless an extraordinary similarity in their 

 chemical character, and especially in their combining tendencies. 

 With oxygen these four bodies produce teroxides and pentoxides 

 which, in combination with water, have all decidedly acid proper- 

 ties. 



The latter acids, moreover, appear to be all tribasic ; in phos- 



