Gay-Lussac’s method

Quantitative Determination. — This may be carried out either gravimetrically by precipitating the silver by means of hydrochloric acid from a boiling solution slightly acid with nitric acid or the determination may be made volumetrically according to Gay-Lussac s method, which is used in all the laboratories of the German mints. 

In a back-titration of silver by chloride ions, potassium chromate can be used to indicate the endpoint (Mohr s method) but with potassium thiocyanate as tifrant, anunonium iron(III) sulfate ( ferric alum ) is preferred. In the direct titration (Gay-Lussac s method) the location of the turbidimetric endpoint has been improved in detail. ... 

In Gay-Lussac s method, 5 g. of the fine powder is mixed with 5 g. dry sodium carbonate. Five g. pure potassium nitrate and 30 g. sodium chlorate are added and the whole well mixed in a mortar, and ignited in a platinum crucible. After cooling, the mixture is dissolved in water, oxidised with bromine solution, acidified, and the sulphate estimated as barium sulphate. 

In this and analogous cases, a question of this nature has to be decided What is the best way to represent the composition of a solution Several methods are available. The right choice depends entirely on the judgment, or rather on the finesse, of the investigator. Most chemists (like Loewel above) follow Gay Lussac, and represent the composition of the solution as parts of substance which would dissolve in 100 parts of the solvent . Etard found it more convenient to express his results as parts of substance dissolved in 100 parts of saturated solution . The right choice, at this day, seems to be to express the results in molecular proportions. This allows the solubility constant to be easily compared with the other physical constants. In this way, Gay Lussac s method becomes the ratio Of the number of molecules of dissolved substance to the number, say 100, molecules of solvent Etard s the ratio of the number of molecules of dissolved substance to any number, say 100, molecules of solution . 

It is a back titration. The excess arsenite is titrated by an iodine solution. This is Gay-Lussac s method. Quite evidently, it is no longer an indirect iodometry. 

While the lead-chamber process increased the amount of sulfuric acid that could be produced, it relied on a source of nitrate that usually had to be imported. The process also produced nitric oxide gas, NO, which oxidized to brown nitrogen dioxide in the atmosphere. To reduce the supply of nitrate required and the amount of nitric oxide produced, Gay-Lussac proposed that the nitric oxide be captured in a tower and recycled into the lead chamber. Although Gay-Lussac first proposed this modification to the lead-chamber method around 1830, it was not until the 1860s that John Glover (1801-1872) actually implemented Gay-Lussac s idea with the Glover tower. 

At the time of their meeting, Liebig, though twenty-one, was professor of chemistry at the small University of Giessen. He had received this appointment through the influence of Von Humboldt, the celebrated scientist, whom he had met in Gay-Lussac s laboratory in Paris. His salary amounted to only one hundred and twenty dollars a year plus about forty dollars for annual laboratory expenses It was here that Liebig invented and developed a method of organic analysis still used today. 

There is another method of viewing chemical proportions, viz. Gay-Lussac s law of volumes i vol. of one gas combines with i, 2, 3, etc. vols. of another. 

In i860 Hofmann adopted the new atomic weights of Gerhardt and Cannizzaro and used them in his lectures. He published over fifty lecture experiments, many for demonstrating the volumetric composition of gases leading to the molecular formulae. His vapour density method was an improvement of Gay-Lussac s (see p. 82). He devised a gas furnace for combustion analysis. ... 

When the news of Davy s isolation of the alkali metals reached Paris in 1808, Napoleon provided Gay-Lussac and Thenard with a powerful voltaic pile. Before it could be set up, however, they showed that these metals can be obtained without a battery simply by reducing the caustic alkali with metallic iron at a high temperature, a method which... 

Lavoisier s investigations had broken the path they had, namely, exploited a method of analysis which was soon improved by Gay Lussac and Thenard, by Saussure, and by Bergelius to attain finally under Liebig s hands such a degree of simplicity and precision that later decades could only retain the method in general, while adding, indeed, for special cases, some modifications. ... 

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