Obfervations on Blue Colours. 93 
of Vitriolated Iron. A large quantity of olive-green 
coagulum appeared. Upon fuperfaturating it, a 
great effervefcence was excited and the whole of 
the coagulum was re-diffolved, yielding a brownifh 
green, diaphanous liquor, but upon ftanding all 
night in the glafs veffel, a brownifh-green precipitate 
fell down. . 
gth. The Acid of Phofphorus was added to the 
Aluminous and Martial Solution, and it gave a pale 
white precipitate. 
1oth. The Acid of Phofphorus being added to the 
Solution of Vitriol of Iron, no decompofition took 
place. . 
It appears that from the Mother-water produced 
from the combination of the Phofphoric Acid and 
Mineral Alkali, a blue colour is always obtained by 
means of a martial Solution; and that from the 
Mother-water of Sal Soda it is uncertain, and 
what is produced is of a pale colour; and that this 
fac might be more fatisfactorily afceriained, the — 
Mother-waters of Sal Soda, that were ufed, 
were thofe from which the Salt had been extracted 
to make the Soda Phofphorata, whofe Mother- 
waters were tried in thefe experiments. 
It is true alfo that the Mother-water of tartarized 
Natron will fometimes yield a Pruifian blue, but 
not always, and whenever it does, it is generally 
pale-coloured; but in all the experiments made 
with the Phofphorated Alkaline Mother-waters above 
related, a deep blue colour has been produced, 
except 
