CHEMICAL SCIEXCE. 285 



The mould around the plants and an infusion of the dead stems and 

 leaves also afforded abundant evidence of the presence of much chlo- 

 ride of sodium. Further inquiry showed that the well from which 

 the water was procured had an accidental communication, by means 

 of a drain, with the sea ; and had thus become mixed with the salt 

 water from that source, and had been used in that state for some 

 weeks, probably from two to three months. From about that time the 

 plants had been observed to droop ; but it was not until nearly the 

 whole of a valuable stock had been destroyed, that any extraordinary 

 cause of the evil was suspected. To place it beyond doubt that the 

 water was really the cause of the mischief, twelve healthy fuchsias 

 were procured from a distance and divided into two parts ; half being 

 watered morning and evening with the water in question, and the oth- 

 ers with rain water. In a week, the six plants watered from the well 

 water turned brown, and ultimately died, while all the rest remained 

 perfectly flourishing. Assuming, from these facts, that the common 

 salt in this water was the chief cause of the results described, it is 

 proved that water containing about seven grains of salt in each pint 

 is, in its continued use, an effectual poison to the weaker forms of 

 vegetation ; or that when a soil is continually watered with a weak 

 solution of salt it gradually accumulates in it until the soil becomes 

 sufficiently contaminated to be unfit to support vegetable life. In 

 either case an interesting subject of inquiry is suggested What is 

 the weakest solution of salt which can produce in any measure this 

 poisonous effect ? or, in other words, at what degree of dilution does 



the danger cease ? 



MEANS OF DETECTING DYES. 



It is not unfrequently desirable to know with regard to a dyed stuff, 

 in what manner it has been dyed, and w r hat dying material has been 

 employed. This cannot always be decided by the appearance : for 

 example, in the case of a dark blue, the question arises whether the 

 ground is pure indigo or pure logwood, or a mixture of both, or 

 whether prussian potash-blue is not present, &c. For this purpose re- 

 course must be had to chemical reagents. 



^j 



In order to ascertain what mordants have been used, the most accu- 

 rate method is to incinerate a sufficiently large piece of the stuff, and 

 examine the ash. 



Blue Colors. These may consist of indigo, logwood, prussian blue 

 or ultramarine. 



Indigo blue is fixed on cloth in various ways : 1st, in the blue vat ; 

 2nd, as so-called China or English blue, blue patterns upon a white 

 ground, fixed, according to the principle of the blue vat, with lime 

 and sulphate of iron ; 3rd, as pencil-blue, the indigo being deoxidized 

 by means of oxide of tin and potash ; and 4th, as soluble indigo. 



The first three blues are not acted upon by diluted acids or "alkalies. 

 By chlorine and nitric, acid, on the contrary, they are destroyed. 

 When the stuffs decolorized by chlorine are washed and dipped in a 



