CHEMISTRY. 



93 



some important facts in regard to the certainty 

 and delicacy of three principal tests for boracic 

 acid. He rejects the test with turmeric as 

 unsatisfactory, in the presence of such a mass 

 of salts as is found in bittern; and he finds 

 the flame reaction by far the most sensitive 

 as well as the most trustworthy of all the tests 

 with which he has experimented. When the 

 Bunsen lamp is supplied with pure hydrogen, 

 he finds that the flame reaction will indicate 

 the one-millionth of a gramme of boracic acid. 

 His method of applying the test is as follows: 

 The material to be tested is first mixed with 

 an excess of oil of vitriol, and this paste, held 

 in a loop of platinum wire, is brought near 

 say within four millimetres, b'ut never nearer 

 than two millimetres to the visible mantle of 

 the hydrogen flame, so that the flame may not 

 be colored in the least by the sodium always 

 present. If the assay contains boracic acid, 

 the characteristic green coloration appears, 

 which can be identified with absolute certainty 

 by means of a spectroscope, and the coloration 

 can be most delicately observed by looking 

 through the mantle of the flame tangentially. 



New Method of preventing Surf ace- Oxidation 

 of Iron. A method proposed by Prof. Barff 

 for preventing the corrosion of iron consists 

 in producing on the surfaces of the iron arti- 

 cles to be protected a coating of the black, 

 or magnetic, oxide of iron. This he does by 

 raising the articles, in a suitable chamber, to 

 a temperature of from 500 to 1,200 Fahr., 

 and then passing steam into this chamber, 

 keeping the articles for 5, 6, or 7 hours, as 

 the case may be, at that temperature, in an 

 atmosphere of superheated steam. At a tem- 

 perature of 1,200 Fahr., and under an ex- 

 posure to superheated steam for 6 or 7 

 hours, the iron surface becomes so changed 

 that it will stand the action of water, even 

 though it be impregnated with the acid fumes 

 of the laboratory. When the process is car- 

 ried on at a lower heat, the iron articles will 

 resist any amount of moisture with which they 

 may come in contact in a house or building; 

 but they will not permanently resist the action 

 of the weather out-of-doors. The reason ot 

 this is, that only a thin film of the iron, on its 

 surface, is transformed into the black oxide. 

 Iron pipes protected by this process may be 

 used instead of lead pipes for conveying water 

 through houses. Iron for architectural uses 

 may be made to resist the weather ; the pro- 

 cess may also be employed to protect cast-iron 

 statues, which would thus be rendered as en- 

 during as those of bronze. 



Reducing Action of Native Sulphurets. 

 From experiments made by Stanislas Meunier, 

 it appears that native sulplmrets, when brought 

 into contact with metallic solutions, reduce 

 the metal from the solution in the free state. 

 For instance, a piece of galena (lead sulphuret), 

 in a solution of silver nitrate, after 48 hours 

 gave rise to beautiful plant-forms of metallic 

 silver ; and gold, mercury, platinum have been 



reduced in the same way. In place of galena, 

 we may substitute the native sulphurets of 

 iron, copper, antimony, mercury, zinc, and even 

 the monosulphide of sodium, which is of such 

 frequent occurrence in mineral waters. These 

 researches appear to throw some light upon 

 certain phenomena observed in mining. Thus, 

 suppose a vein of galena to be subjected, by 

 percolation, to the action of sea-water which 

 always contains silver all the silver in this 

 water will be arrested and concentrated by 

 the sulphuret. Some galenas contain native 

 silver, which we may suppose to have been 

 introduced in this way. Reactions of a like 

 nature may take place in veins of pyrites and 

 other sulphurets. As for sulphureted sodic 

 waters, their agency must have a powerful 

 influence on the production of certain metal- 

 liferous ores. 



Qualitative Determination of Potassa. Car- 

 not offers a new and simple process for the 

 qualitative detection and determination of po- 

 tassa, hitherto one of the most delicate opera- 

 tions of analytical chemistry. It is as follows : 

 In a few drops of hydrochloric acid, one part of 

 the subnitrate of bismuth say half a gramme 

 is dissolved, and then, in a few cubic centi- 

 metres of water, are dissolved about two parts 

 (one gramme to one and a quarter) of crystal- 

 lized hyposulphite of soda. The second solu- 

 tion is poured into the first, and concentrated 

 alcohol added in large excess. This mixture 

 is the reagent. If brought in contact with a 

 few drops of the solution of a potash salt, it at 

 once gives a yellow precipitate. With an un- 

 dissolved potassic salt, it produces a decidedly 

 yellow coloration, easily recognized. All po- 

 tassic salts with mineral acids are susceptible 

 of this reaction ; it is also very sensitive with 

 the organic salts tartrates, citrates, etc. The 

 reaction is not interfered with by the presence 

 of other bases, with which nothing analogous 

 is produced. The character is therefore per- 

 fectly distinct. Baryta and strontia alone may 

 occasion some difficulty, by reason of the white 

 precipitates of double hyposulphites which 

 they form with the same reagent ; but it is 

 very rare to meet them along with potassa, 

 and they are very easily detected and re- 

 moved. 



Artificial Production of Corundum. The 

 artificial production of corundum was the sub- 

 ject of a communication to the Paris Academy 

 of Sciences, by Messrs. Fremy and Feil. The 

 authors dwelt specially upon the methods em- 

 ployed by them in producing crystallized alu- 

 mina of various colors rubies, sapphires, and 

 other gems of the same class in masses suit- 

 able for use by the watchmaker or the lapi- 

 dary. Wishing to follow as closely as possible 

 the natural conditions which, in all probability, 

 attended the formation of corundum, ruby, 

 and sapphire, the authors employed furnaces 

 capable of producing a high temperature^ of 

 maintaining it for a long time, and of treating 

 large quantities of material. They often had 



