_Bases._ _Acids._ Alumina 525 | Fluoric 427 Magnesia 615 | Carbonic 577 Ammoniac 672 | Sebacic 706 Lime 793 | Muriatic (hydrochloric) 712 Soda 859 | Oxalic 755 Strontiane 1329 | Phosphoric 979 Potash 1605 | Formic 988 Baryte 2222 | Sulphuric 1000 | Succinic 1209 | Nitric 1405 | Acetic 1480 | Citric 1683 | Tartaric 1694 It is interesting again to notice how difficult it is for the discoverer of a new truth to find out the most simple and complete statement of his discovery. It looks as if the amount of work needed to get to the top of a new idea is so great that not enough energy remains to clear the very last few steps. It is noteworthy also to observe how difficult it was for the chemists of that time to understand the bearing of Richter's work. Although a summary of his results was published in Berthollet's _Essai de statique chimique_, one of the most renowned chemical books of that time, nobody dared for a long time to take up the scientific treasure laid open for all the world. John Dalton's atomic theory. At the beginning of the 19th century the same question was taken up from quite another standpoint. John Dalton, in his investigations of the behaviour of gases, and in order to understand more easily what happened when gases were absorbed by liquids, used the corpuscular hypothesis already mentioned in connexion with Boyle. While he depicted to himself how the corpuscles, or, as he preferred to call them, the "atoms" of the gases, entered the interstices of the atoms of the liquids in which they dissolved, he asked himself: Are the several atoms of the same substance exactly alike, or are there differences as between the grains of sand? Now experience teaches us that it is impossible to separate, for example, a quantity of pure water into two samples of somewhat different properties. When a pure substance is fractionated by partial distillation or partial crystallization or partial change into another substance by chemical means, we find constantly that the residue is not changed in its properties, as it would be if the atoms were slightly different, since in that case e.g. the lighter atoms would distil first and leave behind the heavier ones, &c. Therefore we must conclude that all atoms of the same kind are exactly alike in shape and weight. But, if this be so, then all combinations between different atoms must proceed in certain invariable ratios of the weights of the elements, namely by the ratio of the weights of the atoms. Now it is impossible to weigh the atoms directly; but if we determine the ratio of the weights