the first contained 19 lbs. 2 oz. of pure dry caustic alkali; 112 lbs. of the second contained 221 lbs. of alkali; and the Teneriffe 223 lbs. which was esteemed much better than is usually brought from that island. Four parcels of barilla which I examined with great care on the 4th of June 1810, were found to be composed as under. The first parcel consisted of 19 parts pure soda, 22 of neutral salts and carbonic acid, and 59 of insoluble matter. The second parcel gave 18 per cent. of pure alkali, 21 of neutral salts, &c., and 61 of insoluble matter. Another contained 103 pure alkali, 24 neutral salts, &c., 65 of insoluble matter, and loss. The fourth parcel consisted of 11 parts of pure alkali, 20 neutral salts, &c., and 69 of insoluble matter. : Two other samples were analysed on the 1st of February 1813 one of which contained 304 per cent. of pure dry soda, 10% neutral salts, 9 carbonic acid and 50 insoluble matter. This was the best sample of barilla that I ever recollect to have come under my examination. Kelp is of very various quality; I have seen some which contained 8 per cent. and others which would not yield one per cent. of pure soda. The particulars of the analysis of several parcels of kelp and barilla which I made for the Highland Society of Scotland in the year 1816 will be found in the 5th vol. of the Transactions of that Society, page 65, &c. 8. Kelp ovens.-Page 39, line 13. The ovens in which kelp is made are generally of the rudest kind, being nothing more than excavations within the ground, lined with rough unhewn stones. I would earnestly recommend it to the proprietors of our kelp shores to erect one or more reverberatory furnaces similar to those described in the plates which accompany the Essay on the fixed Alkalies; for by means of such furnaces a greater heat would be produced, and the matter might be stirred with greater convenience; and hence there would be a more effectual decomposition of the muriate of soda by means of the vegetable alkali which these plants always furnish in abundance. By such management I apprehend much of the Irish and Scotch kelp might be rendered of double its present value. See the plates No. 16 and 17, and the descriptions given of them at the beginning of this volume. 9. Soda for glass.-Page 47, line 16. Since this paragraph was written, I have investigated the nature of the comparative effects of soda and potash in making glass; and I am now convinced that a harder glass may be made with soda than it is possible to produce from potash only, and that soda therefore ought always to be made choice of for making plate glass. See the Essay on Glass, vol. ii. page 245-248. 10. Oil soap.-Page 47, line 20. It is well known that olive oil produces better soap than any other substance. I am therefore anxious to suggest whether it might not be a desirable thing for Government to encourage the growth of olive-trees in some of the British colonies, or in some favourable district in the British settlements in the East Indies. The oil would in time form an important branch of commerce, especially if enough were produced to supply all our soap-manufactories: and this would render the country more independent of Russia; which is a very important object. A competent opinion of the value of this oil for the manufacture of soap, when compared with others, both vegetable and animal, may be obtained by perusing a memoir in the Annales de Chimie, tome xix. pages 289-311. The idea of recommending the cultivation of the olive occurred to me on reading the following passage: "The olive-tree," says Savary, "has almost disappeared from Attica. The Albanians and Turks, who have alternately ravaged Greece, seem to have been intent on destroying it. Within twenty years they cut down two hundred thousand feet of these trees. The island of Crete has not suffered the same fate. The olive-trees, which delight in a sandy soil, a mild temperature, and the vicinity of the sea, grow in abundance on the hills and in the plains. Their produce constitutes the chief wealth of the inhabitants, and their principal branch of commerce. Exclusive of the prodigious consumption of oil by the inhabitants, besides what the Turks of Canea make use of in the manufacture of soap, which they export throughout the Levant, the Turks annually load four-and-twenty ships with oil, containing on an average one hundred and fifty tons each."Savary's Letters on Greece, octavo, 1788, page 381. 11. Sir Humphry Davy.-Page 59, line 8. After this paragraph was printed, I discovered a trifling error in the date which I have given to the first decomposition of the alkalies by Sir H. Davy; for I now perceive that the paper which I mention as having been read before the Royal Society, contained a detail of his subsequent experiments, the discovery itself having been announced in the preceding year (1808), and the particulars of it described in the volume of The Philosophical Transactions for that year. 12. Depositories of salt.-Page 68, line 1. Notwithstanding these immense masses of salt found in various parts of the world, there are places where salt has never yet been discovered: this is the case in many parts of Africa. Mungo Park relates that "the greatest of all luxuries in the interior of Africa is salt. It would," says he, " appear strange to an European to see a child suck a piece of rock salt as if it were sugar. This, however, I have frequently seen; although the poorer class of inhabitants are so very rarely indulged with this precious article, that to say 'A man eats salt with his provisions,' is the same as saying He is a rich man.' I have suffered great inconvenience myself from the scarcity of this article. The long use of vegetable food creates so painful a longing for salt, that no words can sufficiently describe it." Park's Travels into the Interior of Africa, quarto, 1799. Some persons have imagined that it is an useless and pernicious practice to take salt with our food; but the above testimony seems to decide that question. On looking over a work printed by Kearsley, in small octavo, 1768, I find the following experiment is related: "I put," says the author, "two ounces of milk, warm as it comes from the cow, into a tea-cup with a little common salt. I put the same quantity and of equal warmth into another teacup, without salt. Then dropping a very little distilled vinegar into each, a hard curd presently appeared in that milk which had no salt in it, while the other with the salt was scarcely altered." 13. Salt mines of Poland.-Page 68, line 3. fast "We read of a salt mine in Poland, one mile from Cracow, which is 200 fathoms below the surface, where there were 1000 men constantly employed. In order to descend into this stupendous work, it was customary for the person descending to fasten himself by a cord to the main rope, and then to take another man on his lap. The large rope being then lowered a little, a third person made a seat for himself with a rope ened to the main rope, taking another on his lap; and being also let down a little way, he gave an opportunity for another pair to fasten themselves in the same way in which manner thirty, forty, or more people were let down at once; of whom the first having touched the ground at the bottom, steps out and goes aside, the rest following him in regular order and doing the like. Thus they descended to the depth of 100 fathoms; and after passing through several passages they came to certain ladders by which they descended 100 fathoms deeper." Philo sophical Transactions for 1670, page 1099. In the same volume there is an account of the discovery of a mine of very hard rock salt at Rotherton in Cheshire, upwards of 30 yards below the surface of the earth. The salt mine above mentioned is at the town of Wielitska, a German mile from Cracow : it is the largest in Europe, and has been constantly worked for more than 600 years: it is eleven hundred feet in width, and 6,700 feet in length. The subterranean passages or galleries are very spacious, and in many of them altars or chapels are hewn out of the salt-rock. In these chapels, crucifixes or the images of saints are set up; and a light is kept continually burning before them. The places where the salt is hewn out of the mine, are called chambers; and some of these are so spacious that a large church might be inclosed in one of them. When candles are brought into these places, the numerous rays of light reflected by the crystals of salt emit a surprising lustre. About 600,000 quintals of salt are annually dug out of these mines. That part of the mine which has been most excavated, and which appears like a vast plain, is interspersed with clusters of huts belonging to the miners and their families, many hundreds of whom are born and finish their lives in this subterranean inclosure. "There are salt mountains," says Jonston, "in India, particularly at Oxomenus, where it is cut out of quarries like stone; and the custom arising from it is more to their kings than what they receive from gold and pearls." Jonston's History of Nature, p. 94. 14. Decomposition of salt.-Page 68, line 12. Several patents having been obtained at different times by various individuals, for their peculiar methods of procuring soda from sea salt, and having myself many years ago devoted much time and expense to the investigation of this subject, I am glad that I have it in my power to furnish my readers with a list of those patents, which at the time were registered among other chemical manuscripts, as being those which appeared to me to possess the most merit. James King, dated March 4th, - - 1780 George Hodson, February 28th, - - 1797 Mr. Hodson obtained a patent for the same object, which bore date August 30, 1792; but the mode therein described will not effect the desired purpose. While on the subject of Sea-salt, I embrace the opportunity of mentioning a new purpose to which salt has been applied, and which certainly deserves to be registered for the benefit of the public. Some merchants of Liverpool, who in the year 1815 had prepared several hundred carboys of oil of vitriol to be exported to America, had them stowed on board two ships, and filled up all the vacant spaces between the baskets with common salt to prevent the bottles from being broken by the motion of the vessels. Proposals for the insurance of these precious cargoes were sent to Lloyd's, and the circumstance of the stowage in salt was mentioned to induce the underwriters to insure at a lower premium. Some gentleman, however, who knew the effect which would be produced by the affusion of oil of vitriol upon salt, saw the proposals at Lloyd's, and stated that if a single bottle should by any accident become broken on the passage, every individual on board would inevitably be suffocated. It was, however, too late to take any precautionary measures, for the vessels had then both actually sailed. The names of the ships which were then crossing the Atlantic in such a perilous situation were the Lewis and the Margaret, I believe both of Liverpool. Should either of these vessels have sprung a leak, so as to dissolve much of the salt, the stowage of the carboys would have been loosened, and some of the bottles would unavoidably have been broken, by the rocking of the ship.-Here we have another instance how necessary it is that all classes of society should become acquainted with the elements of chemical science. 15. Rock salt.-Page 69, line 3. It is very important to the curers of provisions to employ the purest salt which they can obtain. This is deemed so necessary, that some of the Irish provision-curers have been in the habit of using foreign salt, preferring it chiefly on account of its size and hardness of grain, and imagining that it must on these accounts be better than the English salt for their purpose. It has, however, been proved that the purest and best salt now known is that which is made from the rock salt of Cheshire. It has been usual to dissolve the mineral salt in sea water, and then re-crystallize it; but as sea water besides muriate of soda contains also much muriate and sulphate of magnesia, both which are injurious in the process of curing either flesh or fish, Messrs. Londons of Northwich have obtained a patent for refining rock salt merely by fusing it in a reverberatory furnace. Their salt is therefore without the impurities of sea water, and also without either the water of crystallization or water of adhesion hence it is superior in its purity, solidity, and magni |