I. The monoclinic double sulphates containing ammonium. Completion of the double sulphate series

Abstract

In this communication are described the five remaining double sulphates of the series R 2 M(SO 4 ) 2 . 6H 2 O, in which R is ammonium and M is nickel, cobalt, manganese, copper, and cadmium. The ammonium salts, in which M is magnesium, zinc, and iron, have been described in two previous communications, in the latter of which (that concerning ammonium ferrous sulphate) a number of general questions concerning the whole series were also discussed. The present contribution completes the author’s work, commenced in the year 1890, on the double sulphates of this important monoclinic series, in all 31 salts, of which the It bases have been potassium rubidium, cæsium, ammonium, and thallium. Excluding thallium—of which only the zinc double sulphate has been included, the other double salts containing thallium not having yet been obtained in crystals of the perfection necessary for detailed accurate work of the character regarded as essential by the author—the four bases, potassium, rubidium, cæsium, and ammonium should give rise, with the eight several dyad bases above enumerated, to 32 double sulphates. All these have been obtained in excellent crystals, and fully described, with the two exceptions of potassium manganese and potassium cadmium sulphates, which, for some as yet undiscovered reason, are incapable of preparation. Yet so thoroughly are the relations between the various salts, and the rules governing the replacement of any one alkali base by any other, now understood, that it has been found possible to predict the constants of the two missing salts. Of the isomorphous double selenates, nine salts (including thallium zinc selenate) containing magnesium and zinc as M metals have already been described by the author, and it is intended that the remaining double selenates, those containing the other dyad metals, shall form the subject of the author’s next communication. Morphology . The first measurements of the crystals of this salt were made 60 years ago by Marignac, and the salt was included four years later by Murmann and Rotter in their comprehensive crystallographic investigation. The forms observed in both investigations were the same as those given in the list below, except a {100} and o {111}, and the values observed for the principal angles will be found quoted in the two last columns of the table of angles.