FERRUM (iron) intimately united to a new brittle metal[[71]], or to a peculiar modification of iron, rendering it brittle when cold. Cold-ſhort.
In cold-ſhort iron, a brittle metal exiſts, readily uniting to ductile iron, by the aſſiſtance of heat, but rendering it brittle when cold. This ſubſtance, diſſolved in acids, forms Pruſſian blue with phlogiſticated alkaly, but it is not magnetic: it affords a white calx, richer in phlogiſton than the yellow calx of good iron.
I hope, by more experiments, ſoon to become better acquainted with it.
FERRUM calciforme (iron calciform), phlogiſticated in a peculiar manner. Blue.
Cronstedt Min. § 208. Cæruleum Berolinenſe nativum.
Clay and mould are sometimes coloured ſuperficially by a dilute blue, and ſometimes the former, when newly dug up, is found to acquire this colour upon expoſure to the air. It is evident that the baſis of this colour is an irony matter, full of phlogiſton; for, by ignition upon a charcoal fire, it flames, turns red, and becomes magnetic. With a gentle heat it becomes green, but when melted gives black ſcoriæ.
Alkalies, as well as acids, diſſolve it, and the colour vaniſhes, but appears again, if precipitated from the former by acids, and from the latter by alkalies; but it has then a greenish caſt, and ſoon becomes white. This white ſediment, immerſed in an infuſion of galls, or of tea, recovers its former colour.
From what has been ſaid, it appears that this colour, although analogous to the artificial Pruſſian blue, differs from it in its intensity, in the mode of its production, and in various properties. It keeps its colour in water, but turns black with oil.