Analytical chemistry

“ The new branch of inorganic chemistry called physical chemistry has given us entirely new ideas of the nature of solutions, and the fact that electrolytes in solution are broken up into their constituent ions is one of fundamental importance. ”

“ When he found that each of the known elements, such as copper or oxygen or carbon, consisted ultimately of atoms, all the atoms of any one element being alike, he laid the foundation on which the huge structure of modern chemistry has been raised. The chemist takes one or more atoms of one element, one or more of another, and may be of a third or fourth, and he puts them together into a compound which we call a molecule. ”

“ The view long maintained—until late in the nineteenth century, in fact—that organic and inorganic chemistry are separated from each other by a wide gap, is no longer held. Hundreds of organic substances, some of them of great complexity, have been made in the chemist’s laboratory, and can now be classed as properly with inorganic as with organic substances. The gap has been closed, and there is now but one chemistry. Only the most intricate chemical compounds still lie beyond the chemist’s grasp, and the isolation of these may be at any time overthrown. ”

“ Chemical analysis has not only given us accurate knowledge of the constituents of matter, but by revealing the deportment of molecules and groups of molecules in inorganic and organic compounds, has opened up a path for organic and synthetic chemistry which otherwise must have remained forever closed.
The discovery and development of spectrum analysis is one of the great achievements of the nineteenth century in chemical science. ”

“ If brought into contact with a solution of some substance which will withdraw the hydroxyl ions, converting them into water, or into some non-ionized substance, they are replaced at the expense of the molecules of non-ionized ammonium hydroxide; and these, when diminished in amount, draw on the store of molecules of ammonia and water, which combine, so as to maintain equilibrium, Now the investigation of such changes must belong to the domain of inorganic chemistry. It is true that the methods of investigation are borrowed from the physical chemist ”

“ But that is a matter of inorganic chemistry, you say. Very true. But I dare to assert, standing here on my two feet, that in the organic I can duplicate whatever occurs in the inorganic.
“Here!” He held a test-tube between me and the light, and I noted the cloudy or muddy liquid it contained. He emptied the contents of another test-tube into it, and almost instantly it became clear and sparkling.
“Or here!” With quick, nervous movements among his array of test-tubes, he turned a white solution to a wine color, and a light yellow solution to a dark brown. ”

“ Thus, even in Chemistry, limits are set to the successful adoption of the purely mechanical point of view, by the fact that chemical combination is regularly productive of new qualities in the compound which could not have been predicted from a knowledge of the properties of its constituents, but have to be ascertained a posteriori by actual experiment. ”

“ The properties of matter are so distributed among the elements that three of them—Oxygen, Hydrogen, and Carbon—possess an ensemble of unique characteristics. The number of reactions in inorganic chemistry are relatively few, but in organic chemistry—in the chemistry of these three elements the number of different compounds is practically unlimited. ”

“ The theory of the atom and the molecule forms the second division of the work, this doctrine being tested and exemplified by the phenomena of refraction, polarization, magnetism, color, dissociation of gases, and the behavior of both colloids and crystalloids in solution. The transformation of matter and the transformation of energy are the two remaining division-, the former embracing the laws of chemical statics and chemical kinetics, while the latter is concerned mainly with thermo-chemistry, though touching upon the chemical action of light and electricity. ”

“ Scientists talk of electrons and protons as the two elemental forces and of the mechanics of the atom. In chemistry, investigation follows the problems of applied chemistry, while organic chemistry or biochemistry opens continually new fields of research. ”

“ The study of the structure of molecules naturally leads to the study of their stability, and of the conditions which determine chemical changes, and thus opens the recently explored field of thermo-chemistry. To be able to predict the order and results of possible conditions of association of materials, or of chemical changes under all circumstances, is now the highest aim of our science, and we have already made very considerable progress toward this end. ”

“ So the organic body is built on a chain or frame-work or skeleton of carbon atoms, about which are grouped the atoms of hydrogen, oxygen, and nitrogen, or radicle compounds thereof.
It is not possible here to even name some of the more eminent workers who for a quarter of a century have contributed to our knowledge of organic chemistry. This branch of chemistry has been the vogue, and has been pushed almost to the limit of possibility since 1875. ”

“ However large the masses changed by chemical action, that action is always on the individual molecule, the atoms of which are separated. If the molecule were an indivisible particle, no science of chemistry would be possible. The physicist finds the properties of masses of matter and resolves them into molecules, the chemist breaks up the molecule and from its atoms builds up other compounds. ”

“ We now know that matter is not indefinitely divisible, and that the smallest parts of the various simple substances existing in those that are naturally compound have not all the same dimensions, nor equal weights. Chemistry, by a course of analyses and measurements, has succeeded in determining the weights of atoms of the different elements, that is to say, taking as a unit an atom of the lightest element, hydrogen, in determining the weight of the atoms which are equivalent to this conventional unit in the various combinations. ”

“ These compounds, resolved into their elements by the processes of chemistry, yield a certain number (fifty-five) of substances which, under the conditions yet applied to them, are found to be incapable of further analysis, and are therefore called simple or elementary substances. They are singularly diversified in weight, mode of existence when separate, and relation to temperature and electricity.
In a free state under ordinary pressure and temperature, some (five) exist as gas; viz., hydrogen, oxygen, chlorine, fluorine, azote. Seven are non-metallic solids and liquids ”

“ Much also has been done in the way of building up compounds the existence of which was predicted by theory. Indeed, the extent to which hitherto undiscovered substances can be predicated is doubtless the greatest triumph achieved by chemists during the past fifty years. As yet, however, only the statical side of chemistry has been developed. While the physicist has been engaged in tracing, for the gaseous condition at least, the paths of the molecules and calculating their velocities, the chemist, whose business is with the atoms within the molecule, can point to no such scientific conquests. ”

“ This doctrine may be illustrated Modern Pythagorisms in chemistry. by facts familiar to chemists, who, in like manner, attach significant numbers to the names of things. Taking hydrogen as unity, 6 belongs to carbon, 8 to oxygen, 16 to sulphur. Carrying those principles out, there is no substance, elementary or compound, inorganic or organic, to which an expressive number does not belong. Nay, even an archetypal form, as of man or any other such composite structure, may thus possess a typical number, the sum of the numbers of its constituent parts. ”

“ The discovery, prognostication, and, in general, the study of such indirect methods of the preparation and formation of substances forms one of the existing problems of chemistry. From the fact that A does not act at all on B, it must not be concluded that a compound AB is not to be formed. The substances A and B contain atoms which occur in AB, but their state or the nature of their motion may not be at all that which is required for the formation of AB, and in this substance the chemical state of the elements may be as different as the state of the atoms of oxygen in ozone and in water. ”

“ In chemistry, in determining the standard atomic weights of bodies, it seems easily and completely applicable, by a process which will suggest itself at once to every chemist, and seems the only thing wanting to place the exactness of chemical determinations on a par with astronomical measurements. ”

“ To these questions we can only answer, by referring to the history of chemistry;—by pointing out what chemists have understood by analysis, according to the preceding narrative. They have considered, as the analysis of a substance, that elementary constitution of it which gives the only intelligible explanation of the results of chemical manipulation, and which is proved to be complete as to quantity, by the balance, since the whole can only be equal to all its parts. It is impossible to maintain that new substances may not hereafter be discovered ”

“ The chemist says, you cannot discover all the properties of hydrogen and oxygen by examining these substances apart from one another, for one of the most important properties of either is manifested only when the two mutually react: the formation of water is not the destruction of the properties of hydrogen and oxygen and the revelation of their essential substrata, it is rather the manifestation of a property of each which cannot be discovered except by causing the union of both. ”

“ The formation of solutions may be considered in two aspects, from a physical and from a chemical point of view, and it is more evident in solutions than in any other department of chemistry how closely these provinces of natural science are allied together. On the one hand solutions form a particular case of a physico-mechanical interpenetration of homogeneous substances, and a juxtaposition of the molecules of the substance dissolved and of the solvent, similar to the juxtaposition which is exhibited in homogeneous substances. ”

“ For a similar reason the study of inorganic chemistry naturally precedes the study of organic chemistry, because inorganic compounds are much simpler and therefore more easily analysed and investigated than organic compounds. ”

“ Numerous considerations compel us to renounce the idea of statical equilibrium in molecules, and the recent yet strongly-supported appeals to dynamic principles constitute, in my opinion, the foundation of the modern teaching relating to atomicity, or the valency of the elements, which usually forms the basis of investigations into organic or carbon compounds. ”

“ The analysis of organic compounds is probably best taught in connection with the course in organic chemistry. It is here that the student is introduced to the use of the combustion furnace and the method of working out the empirical formulæ of the compounds which he has carefully prepared and purified. The laboratory practice in organic chemistry generally requires the use of larger pieces of apparatus. ”

“ Numerous phenomena of even a more striking character than those selected, are exhibited in every department of chemistry; but within the limits of this essay it is impracticable to speak of any beyond those which directly explain natural phenomena.
The chemical elements, which actually exist in nature as simple bodies, are probably but few. Most of the gases are in all probability compounds of some ethereal ultimate principles; and with the advance of science we may fairly hope to discover the means of reducing some of them to a yet more simple state. ”

“ Although there can be no doubt that this doctrine greatly stimulated the pursuit of organic chemistry, it was gradually perceived that to regard inorganic and organic chemistry as the chemistry respectively of the simple and of the compound radicals was an imperfect and misleading conception of the true relations of the two main divisions of the science. Facts showed that the properties of a substance depend more on the arrangement of its atoms than on their nature. ”

“ Definition of valence. A study of the formulas of various binary compounds shows that the elements differ between themselves in the number of atoms of other elements which they are able to hold in combination. This is illustrated in the formulas
It will be noticed that while one atom of chlorine combines with one atom of hydrogen, an atom of oxygen combines with two, an atom of nitrogen with three, one of carbon with four. ”

“ The practical side of organic chemistry should never be lost sight of for a moment, and under no condition should the course be allowed to deteriorate into one of mere picturing of structural formulæ on the blackboard. All chemical formulas are merely compact forms of expression of what we know about chemical compounds. There are, no doubt, many facts about chemical compounds which their accepted formulas do not express at all, and the wise teacher should lead the student to see this. ”

“ To the physicist matter is presented in three leading forms—solids, liquids and gases; and although further subdivisions have been rendered necessary with the growth of knowledge the same principle is retained, namely, a classification based on properties having no relation to composition. The fundamental chemical classification of matter, on the other hand, recognizes two groups of substances, namely, elements, which are substances not admitting of analysis into other substances, and compounds, which do admit of analysis into simpler substances and also of synthesis from simpler substances. ”