oj a Lake near Lidotin, in South Prussia. 2-igi 



tlbits on its smooth surface, when exposed to the light, a 

 cupreous colour. The phenomenon also observed in re- 

 aard to indioo, that when strewed over coals the smoke 

 which rises immediately from it, when viewed against the 

 litrht, has a beautiful lidit red colour, mav be connected 

 with the same causes. 



This phaenomenon is not so uncommon as seems generally 

 to be believed. A few years ago I had an opportunity of making 

 similar experiments on water found in a lake at Strautzberg, 

 not far from Berlin. The same circumstances were observed 

 here, and in the same season, namely, the winter. The 

 water of the lake was in some places coloured red, blue, and 

 green ; and masses of the sam^e colours floated about in the 

 parts of the water which were colourless. In flasks which 

 were filled with the water and transmitted to n)e, the co- 

 loured part of the water gradually separated itself and as- 

 cended, while the water at the bottom remained colourless. 

 The phaenomena which took place in the course of my ex- 

 periments were exactly similar to those which occurred in 

 my researches respecting that of the lake near Lubotin. In 

 January 1799 ^Ir. Achard \\aA an opportunity to subject 

 the water of this lake, supposed to be converted into blood, 

 to some experimci\ts also, from which he concluded that 

 the colouring matter consisted of some vegetable substance, 

 and floated in the water but was ncU properly dissolve-d in 

 it. The small quantity which he had obtained of this water 

 did not permit him to piake any further experiments of a 

 more decisive nature. 



A similar phaenomcnon had been before observed several 

 times in the lake near Strautzberg. According to an ac- 

 count published by Mr, Campe, a clergyman at Alt-Lands- 

 berg, in the Physica/ischcri Bth/sligirngm^', he saw in the. 

 year 1737 the water of that arm of the lake which proceeds 

 towards the town entirely of a red colour. Fifteen years 

 after, the lake in the same place appeared to be wholly 

 green. In the course of two days the water had resumed 

 its usiial colour. The water put mto flasks, which at first 

 was somewhat red, gradually became putrid ; soon after it 

 was thick and muddy ; and at the end of some weeks there 

 was separated from it a dark red mass which floated on the 

 surface. In the present case it appeared of two colours ; 

 when turned from the light, opake and dark red ; when 

 turned towards the light, dark green. This green colour 

 observed by Campe is, however, not essentially dilfercut 



♦ Part xi. Berlin 1751. 



from 



