328 CHEMISTRY. 



Sehunck has obtained this yellow colouring matter which aeems applicable to 

 dying purposes, from the leaves of the buckwheat {Polygonum fag opyr urn). He 

 denies the existence of indigo in this plant. It appears to be the same substance 

 as Rutine, Ilixanthin, and the body obtained from capers. The leaves contain 

 about one thousandth part of the colouring principle. 



SULPHATE OF BARYTA. 



It has been mentioned in a former number that this salt is now extensively used 

 as a substitute for white lead, but in order that it may be so employed it must be 

 obtained by precipitation in an amorphous condition. In the process mentioned 

 ante vol. iii., p. 521, the native sulphate is employed, but the carbonate may be dis- 

 solved in hydrochloric acid and precipitated by sulphuric acid. Pelouze has shown 

 that the solid carbonate, without previous pulverization, may readily be converted 

 into sulphate of the greatest tenuity, by digesting it with dilute sulphuric acid to 

 which three or four per cent, of hydrochloric acid have been added. 



This latter acid acts as a carrier of the baryta to the sulphuric acid, without it 

 the process soon stops ; its action is similar to that of the acetic acid in the Dutch 

 process for manufacturing white lead. 



It is curious that marble is not acted on in the same way, even a large quantity 

 of hydrochloric acid scarcely increases the action at all. 



DETECTION OF BLOOD STAINS. 



Teichmaun discovered that by the action of acetic acid upon blood crystals of 

 the colouring matter may be obtained. Briicke finds that this test can be employ- 

 ed on exceedingly minute traces, the course adopted being as follows : 



Some of the fluid obtained by exti-acting the spot with distilled water is put 

 into a watch glass, mixed with a few drops of solution of chloride of sodium, and 

 left to dry under the air pump with sulphuric acid. It is then inspected under the 

 microscope to ascertain that nothing is there that could be confounded with 

 Teichmann's crystals. The residue is then treated with glacial acetic acid and 

 evaporated to dryness at a temperature of 212° F. A few drops of water are 

 added, and the whole placed under the microscope. Crystals will then be apparent 

 if blood were present. 



OZONE. 



Tait and Andrews have found if electrical sparks be passed through dry oxygen 

 not more than one hundredth part is converted into ozone. A greater effect is 

 produced by the silent discharge and a diminution of volume takes place amount- 

 ing in one case to one thirty-fifth. On heating to 250'' C, so as to destroy the 

 ozone, the gas re-acquired its original volume. Hence the density of the modified 

 oxygen thus obtained must be greater than in its unchanged condition, and it ap- 

 pears that it is also greater than it is in the ozone procured by electrolysis. 



Mercury in contact with ozone loses its mobility to a great extent, and may be 

 made to cover the surface of the tube with a fine reflecting surface. 



The authors state that the discharge from the induction coil produces very insig- 

 nificant ozonic effects. (This statement seems to require verification, as all who 



