The year 1815 saw the completion of the research on cyanogen already referred to, and with it concludes the period of Gay-Lussac’s most important discoveries. Having now attained a leading if not the foremost place among the scientific men in the French capital, his advice was often required on important questions. His attention was thus turned in part from purely scientific subjects to points of practical interest. In these new fields, however, he dis- played the same powers which he had exercised so sedu- lously in the pursuit of scientific truth; in fact he was now to introduce and establish scientific accuracy where there had been previously only practical approximations. The most important of these later discoveries were the method of estimating the amount of real alkali in potash and soda by the volume of standard acid required for neutralization ; the method of estimating the amount of available chlorine in bleaching powder by a solution of arsenious acid ; direc- tions for the use of the centesimal alcoholometer, published in 1824, and specially commended by the commission of the Institute appointed to report on it, as displaying all the accuracy and exhaustive treatment of the author; and lastly, the perfecting of the method of assaying silver by a standard solution of common salt, a volume on which was published in 1833. This last has superseded the old method of assaying silver by cupellation, as being more rapid, more accurate, and easier of execution; and indeed all these processes are so complete and satisfactory, and are besides so identified with their author’s name, that his reputation is secured by them, quite independently of his earlier work. In what has been said above, only the more important of Gay-Lussac’s discoveries have been alluded to. To enter into an account, however brief, of all his labours, would occupy more space than can be allowed here. Indeed the list of his papers in the Royal Society’s catalogue amounts to 148, besides those of which he was joint—author with You Humboldt, Thénard, Welter, and Liebig ; and they embrace every department of the science as cultivated fifty years ago. Among his later researches may be mentioned those on fermentation, and those executed by Liebig in conjunction with him, after the young German chemist had gained the coveted admission to Gay-Lussac’s private laboratory during the years 1823- 24. The latter include improvements on organic analysis, and the examination of fulminic acid. Gay-Lussac con- tinued his work, and published the results in the Annales de C'lzimie, of which he had been joint-editor for some thirty years, up till almost his death, which took place at Paris on May 9, 1850.
Some of the appointments he held have been already referred to. After having acted as Fourcroy’s demon- strator, he was made professor of chemistry at the Ecole Polytechnique. From 1808 to 1832 he was professor of physics at the Sorbonne, and he only resigned that office when he was made professor of chemistry at the Jardin des Plantes. Besides being on the commission of arts and manufactures, and the “administration ” of gun- powder and nitre, he was appointed assayer for the mint in 1829. In 1831 he was elected to the chamber of deputies as member for Haute Vienne, and finally, in 1839, entered the chamber of peers.
Gay-Lussac’s scientific work is remarkable not only for its range but for its intrinsic worth, its accuracy of detail, its experimental ingenuity, its descriptive clearness, and the soundness of its inferences. He did not hesitate to criticize his own results, and replace them by others more accurate either of his own or of another’s discovery; be improved and invented physical and chemical apparatus: the bare- meter, thermometer, cathetometer, alcoholometer, and the burette, which still bears his name, all bear witness to his ingenuity and practical skill. He devised new analytical methods; he discovered new substances, such as fluoride of boron, and iodic, hydrosulphocyanic, dithionic, and hyposulphurous acids ; he enlarged and corrected the knowledge of those already discovered; he examined the physical conditions of chemical action; he searched into the causes of chemical combination and chemical change. That he had the power of grasping the law underlying a few facts is nowhere more evident than in the memoir on gaseous combination, his most important contribution to science. That he missed the opportunity of assigning the chief limit to Lavoisier’s hypothesis, must be ascribed partly at least to the influence of others. Authority decided it, perhaps against his secret convictions.
From Arago’s and other notices one gathers that Gay- Lussac was reticent, patient, persevering, accurate to punctiliousness, perhaps a little cold and reserved, and not unaware of his great ability. But he was also hold and energetic, not only in his work, but equally so in defence and support of his friends. His earliest childish adven- tures, as told by Arago, herald the fearless aeronaut and undaunted investigator of volcanic eruptions. The en- durance he exhibited under the laboratory accidents which befell him shows the power of will with which he could face the prospect of becoming blind and useless for the prosecution of the science which was his very life, and of which he is one of the most distinguished orna- ments. It was only at the very end, when the disease from which he suffered left him no hope, that he complained with some bitterness of the hardship of leaving this world when so many discoveries were making, and when so many more were likely to be made.
The more important of Gay-Lussac’s papers are scattered through journals difficult of access. The most complete list of them is con- tained in the Royal Society’s catalogue of scientific papers; lists are also given at the end of Hocfer’s article in the Biographz’e G’ém’mle, and in Poggendorff' s Biographisch-lz'terarisclzes Hand- worterbuch, Leipsic, 1863. Accounts of various portions of Gay- Lussac’s discoveries and views will be found in such works as Thomson's History of Chemistry, vol. ii., London, 1830; Kopp's Gcschichtc dcr Chem-ta, Brunswick, 1843—47; Kopp's Enta'z'ckcl- mtg dcr Chemie, Munich, 1871 ; Dumas, Legons sur la Philosophies Chtmiqur, Paris, 1837, and reprinted Paris, 1878; Ladenburg, V ortn‘igc fiber die Mttwiekelungsgeschichte der Chemz'c, Brunswick, 1869; Forbes, A Review of the Progress of Mathematical and Physical Science in more recent times, Edinburgh, 1858. The chief authorities for the life of Gay-Lussac are Arago (Graves, Paris, 1855, t. iii.); Biot (Abstracts, Royal Society, vol. 17., 1843—50, p. 1013); P. A. Cap (Le Muse'um d’Histoz're Naturelle, Paris, 1854, pt. 1, p. 137).
to the south boundary of the Holy Land. The Hebrew is more correctly rendered in English as Azzah (Deut. ii. 23), and means “strong.” The modern Arabic form of the name is Ghazzeh. The town stands on an isolated hill about. 100 feet high, and has now a population of 1800 souls. It is divided into four quarters, the eastern Suburb consisting entirely of mud houses. A magnificent grove of very ancient olives forms an avenue 4 miles long north of the city. On the south-east are a few palms. There are many lofty minarets in various parts of the town, and a fine mosque built of ancient materials. A 12th century church towards the south side of the bill has also been converted into a mosque. On the east is shown the tomb of Samson (an erroneous tradition dating back to the Middle Ages). The ancient walls are now covered up beneath green mounds of rubbish. The water supply is from wells sunk through the sandy soil to the rock; of these there are more than twenty—an unusual number for a Syrian town. The land for the 3 miles between Gaza and the sea consists principally of sand dunes. There is no natural harbour, but
traces of ruins near the shore mark the site of the old