2§(J iCIENTU'lC NEV.'f. 



SCIENTIFIC NEWS. 



Oh/tT^vations on St. John's Wort. Bij Cit. Baunach.* 



The juice of OT. JOHN's wortj hi/pericuvt perforatum, is arefinous plantp" 

 St. John's woit (lie tops and flowers of" which contain a juice folublein water, 

 colour, afcoholj and virtegar. With the former two it gives a blood- 



andalfoayel- red colour, with the laft a fine bright Crimfon* When com- 

 '°'"' bined with [mineral?] acids or metallic folutions, it affords a: 



yellow colour, which proves, that it contains two colouring 

 Red moftfolu- matters, one, the red, more foluble than th,e other. 

 IWo'de of dyeing ^^ dye linen, woollen, filic, or cotton yellow^ it is fufficient 

 with.it. to put them into a bath, the water of which is duly impreg- 



nated with the juice of this plant, with a certaift quantity of a 

 mordant. The beft mordant for this colour is alum combined 

 milh a fuitable portion of potafh. The ftufFmufl be left in the 

 bath fometime; for the durability of the colour, and the fhade 

 produced, depend chiefly on the time of continuance in the 

 bath, the quantity of the mordant, and the degree of heat 

 Various lints employed. When but little mordant is ufed, the tint is a bright 

 P!,adaced by it. yellow ; by increafing it the colour is made to incline to green j 

 and on adding a folution of tin in nilro-mnriatioacid, italTumes 

 Alumandpotafii rofe, cherry, and crinifon hues, all with a fine luftre. Alum 

 form the proper ajone does not anfwer well, the addition of potafh being efTen- 

 tial. This decorapofes the alum, precipitates its earth, dif- 

 folves a confiderable portion of it, and this alca-lrne (alt with 

 an earthy bafe becomes the true mordant in the procefs ; the 

 more becaufe the colouring principle refides in a fubfiance a!» 

 mofi: purely refinous. 

 Srains paper The juice of St. Johns's wort, united with the mordant here 



^^''°*' mentioned gives a fine yellow colour to paper; and as it pro- 



arid dyes leather, duces the fame effe6t on leather, it may be employed with ad- 



I'antage for dying (iTeep and other while fkins. 

 Contains tan- The plant contains a confiderable quantity of tannin, as I 



"'"• . have been convinced by means of the folulion of glue, and 



other experiments made for this purpofe. 

 Sulphate of iroa On dropping a little folution of fulphate of iron into the juice 

 converts it into of St. John's wort, a blackifh broVvn precipitate is formed, 

 a concrete refin. , . , . , , /• i /■ i ■ ' i 



which has the property of ablorbing oxygen, becommg at 



length infolublein water, and alTuming the characters of a con- 

 erete refin. 



* Fronj the Annales de €bimie, 



y Having 



