1823.] On the Crystalline Forms of Artificial Salts. 449 



Or, 



Sulphate of iron 43-84 



Sulphate of alumina 12*88 



Water 43-28 



100-00 



Article IX. 



On the Crystalline Forms of Artificial Salts. 

 By H.J.Brooke, Esq. FRS. 



(To the Editor of the Annals of Philosophy.) 



DEAR SIR, 



Th e introductory volume to the Science of Crystallography 

 on which I have been for several months engaged, having passed 

 through the press, 1 propose now to resume an examination of 

 the crystalline forms of the artificial salts, a subject which has 

 been hitherto much neglected, and of which, during the last two 

 years, we have frequently spoken. 



As an evidence of the neglect with which the crystallographi- 

 cal characters of the productions of the laboratory have been 

 treated, 1 may refer to the recent edition of Dr. Henry's Che- 

 mistry ; and 1 do this, not to impeach in the slightest degree 

 the value of that work, but merely to remark, that instances of 

 imperfect and useless descriptions of crystalline forms are admit- 

 ted into volumes otherwise of great worth. 



The crystalline characters of the artificial salts will, if strictly 

 attended to, frequently assist the researches of the chemist. 



An examination of the forms, and measurements of the angles 

 of the crystalline deposits from his experimental processes, will 

 immediately inform him whether his experiments have produced 

 such results as he had anticipated, or whether his compounds are 

 new and unexpected. For this purpose, however, the reflective 

 goniometer must be added to his other implements, and he will 

 not fail soon to discover its value in reference to his pursuits. 



But to be provided with the- means of effectually applying 

 this instrument, he must be acquainted with the forms, and 

 the measurements of the angles of all the known crystals 

 of those salts. During the last summer, I measured a consider- 

 able number of these, most of which I have to thank you for 

 procuring for me, and for some others I am indebted to the 

 kindness of Mr. Teschemacher. Several I also prepared myself; 

 and 1 shall still feel obliged to you, or to any of your friends, for 

 measurable crystals of any of these artificial compounds. 



New Series, vol. v. 2 o 



