« ElőzőTovább »
composed, which of course would increase their volume and their absolute weight *. In supposing ammonia a triple compound of nitrogen, hydrogen, and oxygen, it is no less easy to give a rational account of the phaenomena of its production and decomposition, than in adopting the generally received hypothesis of its composition. - Oxygen, hydrogen, and nitrogen are always present in cases in which volatile alkali is formed; and it usually appears during the decomposition of bodies in which oxygen is loosely attached, as in that of the compounds of oxygen and nitrogen dissolved in water. At common temperatures, under favourable circumstances, the three elements may be conceived capoble of combining and of remaining in union: but at the heat of ignition the affinity of hydrogen for oxygen prevails over the complex attraction, water is formed, and hydrogen and nitrogen are evolved; and, according to these conclusions, ammonia will bear the same relations to the fixed alkalies, as the vegetable acids with compound bases do to the mineral ones with simple bases. Oxygen then may be considered as existing in, and as forming an element in all the true alkalies; and the principle of acidity of the French nomenclature, might now likewise be called the principle of alkalescence. From analogy alone it is reasonable to expect that the alkaline earths are compounds of a similar nature to the fixed alkalies, peculiar highly combustible metallic bases united to oxygen. I have tried some experiments * In the present state of our knowledge, perfectly correct data for proportions cannot probably be gained in any experiments on the decomposition of ammonia, as it seems impossible to ascertain the absolute quantity of water in this gas; for electrization, according to Dr. Henry's ingenious researches, offers the only means
known of ascertaining the quantity of water in gases, upon upon barytes and strontites; and they go far towards proving that this must be the case. When barytes and strontites, moistened with water, were acted upon by the power of the battery of 250 of 4 and 6, there was a vivid action and a brilliant light at both points of communication, and an inflammation at the negative point. In these cases the water might possibly have interfered. Other experiments gave, however, more distinct results. Barytes and strontites, even when heated to intense whiteness in the electrical circuit by a flame supported by oxygen gas, are non-conductors; but by means of combination with a very small quantity of boracic acid they become conductors; and in this case inflammable matter, which burus with a deep red light in each instance, is produced from them at the negative surface. The high temperature has prevented the success of attempts to collect this substance; but there is much reason to believe that it is the basis of the alkaline earth employed. - Barytes and strontites have the strongest relations to the fixed alkalies of any of the earthy bodies *; but there is a chain of resemblances, through lime, magnesia, glucina, alumina, and silex. ...And by the agencies of
* The similarity between the properties of earths and metallic oxyds was r ed in the carly periods of Chemistry. The poisonous nature of barytes, and the great specific gravity of this substance as well as of strontites, led Lavoisier to the conjecture, that they were of a metallic nature. That metals existed in the fixed alkalies seems, however, never to have been suspected. From thcir analogy to ammonia, nitrogen and hydrogen have becn supposed to be amongst their elements. It is singular, with regard to this class of bodies, that those most unlike metallic oxyds are the first
which have been demonstrated to be such. batteries
batteries sufficiently strong, and by the application of proper circumstances, there is no small reason to hope, that even these refractory bodies will yield their elements to the methods of analysis by electrical attraction and repulsion. In the electrical circuit we have a regular series of powers of decomposition, from an intensity of action so feeble as scarcely to destroy the weakest affinity existing between the parts of a saline neutral compound, to one sufficiently energetic to separate elements in the strongest degree of union, in bodies undecomposeable under other circumstances. When the powers are feeble, acids and alkalies, and acids and metallic oxyds, merely separate from each other; when they are increased to a certain degree, the common metallic oxyds and the compound acids are decomposed; and by means still more exalted, the alkalies yield their elements. And as far as our knowledge of the composition of bodies extends, all substances attracted by positive electricity are oxygen, or such as contain oxygen in excess; and all that are attracted by negative electricity are pure combustibles, or such as consist chiefly of combustible matter. The idea of muriatic acid, fluoric acid, and boracic acid containing oxygen, is highly strengthened by these facts. And the general principle confirms the conjecture just stated concerning the nature of the earths. In the electrization of boracic acid moistened with water, I find that a dark-coloured combustible matter is evolved at the negative surface; but the researches upon the alkalics have prevented me from pursuing this fact, which seems, however, to indicate a decomposition. Muriatic Muriatic acid and fluoric acid in their gaseous states are non-conductors; and as there is every reason to be:ave that their bases have a stronger attraction for oxygen than water, there can be little hope of decomposing them in their aqueous solutions, even by the highest powers. In the electrization of some of their combinations there is, however, a probability of success. An immense variety of objects of research is presented in the powers and affinities of the new metals produced from the alkalies. In themselves they will undoubtedly prove powerful: agents for analysis; and having an affinity for oxygen stronger than any other known substances, they may possibly supersede the application of electricity to some of the undecompounded bodies. The basis of potash I find oxydates in carbonic acid, and decomposes it, and produces charcoal when heated * in contact with carbonate of lime. It likewise oxydates in muriatic acid; but I have had no opportunity of . making the experiment with sufficient precision to ascertain the results. In sciences kindred to chemistry, the knowledge of the nature of the alkalies, and the analogies arising in consequence, will open many new views; they may lead to the solution of many problems in geology, and shew that agents may have operated in the formation of rocks and earths which have not hitherto been suspected to exist. t It would be easy to pursue the speculative part of this enquiry to a great extent; but I shall refrain from so occupying the time of the Society, as the tenour of my object in this lecture has not been to state hypotheses, but to bring forward a new series of facts. An
An Account of a Method of hastening the Naturation of
Grapes. By JOHN WILLIAMS, Esq. In a Letter to the Rt. Hon. Sir Joseph BANKS, Bart.
K. B. P. R. S. Si. From the TRINSACTIONS of the HORTICULTURAL
Society of London.
IT is a face well known to gardeners, that vines, when exposed in this climate to the open air, although trained to walls with Southern aspects, and having every advantage of judicious culture, yet in the ordinary course of our seasons ripen their fruit with difficulty. This remark, however, though true in general, admits of some exceptions, for I have occasionally seen trees of the common white muscadine, and black cluster grapes, that have matured their fruit very well, and earlier by a fortnight or three weeks, than others of the same kinds, and apparently possessing similar advantages of soil and aspect.
The vincs that ripened the fruit thus early, I have generally remarked, were old trees having trunks cight or ten feet high, before their bearing branches commenced. It occurred to me, that this disposition to ripen early might be occasioned, by the dryness and rigidity of the vessels of the old trunk, obstructing the circulation of that portion of the sap, which is supposed to descend from the leaf. And to prove whether or not my conjectures were correct, I made incisions through the bark on the trunks of several vines growing in my garden, removing a circle of bark from each, and thus leaving the naked alburnum above an inch in width completely exposed; this was done in the month,