stands a t the head of the list. Fortunately, howevcr, it may be subjugated so that elutriation can continue in water in n o m 1 fashion. The treatment required is a simple one. Dichromate has long been known to deaden the surface of galena. By the use of it. lead concentrates have been made completely docile. In the first step of preparation the sample is treated with a very dilute solution of sodium dichromate, acidified with sulfuric acid. when the dichromate solution has spent its oxidizing strength (only a few minutes are required). gum arabic is added and the sample is vigorously shaken to complete the deflocculation. Then the wet screening and all the subsequent steps in elutriation will follow with all the precision desired.
The design was evolved after conference with G. G. Griswold. Jr., research engineer for the Anaconda Copper Mining Company, who has used this type of elutriator for the study of mill products. The apparatus is similar to the type described in our paper except that a piezometer is used to control the overtlow. The elutriator wm made from a 250-ec. dispensing burrt. Once calibrated, the piezometer permits rapid setting of the apparatus to secure the desired acetone velocities. An elutriator of the above JcT sire may be used throughout the W I L LH. COOE~ILI. range from 150 to 1600 mesh (1W MlsILs5lrrl VnLLsv l i n i ~ a x l n a i rsrarcoh. to 9rr for quartz). U. S. B U R E A U or MINES, R o ~ m Me. , Uercmb~r31. 1030 It has been found convenient Grst to deslime in water the mate. ..,. rial to be elutriated in acetone Editor OJ IndurLrlal and Engineering Citemislry: This allows the acetone t o be used We are in accord with Mr. Coghill’s statement onceruiiig several times before it is nceessaw to purify it by distillation Con the use of a slightly acid solution of dichromate to deaden tlir surface of galena so tiiat i t may he elutriated in water. We sidcrable economy of amtone i‘ cfTccted, since the d i s t i l l a t i o i i have used the method. losses are rather high with ortii Figure 1 shows a galena pastide whose surface was treated nary laboratory equipment. in an acid dichromate saliition after protecting i t in part witlr E. J. Hall, of Colambia I n i paraffin. The paraffin was removed before photographing. versity, has suggested the use oi The dull portion is that which was etched by the dichromate. Its appearance is due to the formation of lead chromate or a tap water freed of dissolved gases by a V B C U U ~ pump in place of CLAMP mixture of lead chromate and lead sulfate. Our objection to treating galena in the maniier suggested by d i s t i l l e d water. Such watcr is Figure 1 Mr. Cogkiil is twofold Firstly. i t makes analysis for lead in suitable if it does not contain the elutriated products somewhat more difficult. owing to tlic sufficient dissolved substances to cause flocculation or to intruchromate radical. Secondly, some of the coating from the duce adsorbed foreign salt3 in the finest fraction of an elutriated coarse particles may slough off,increasing the lead content of sample. the finest grade. Also, some lead appears to go into solution A. M. GAUDIN and to he precipitated iu the solution, atid not a t the surface J. 0. GROW of the galeria particle-. H. B. H n ~ o s x s o ~
.
MONTANA
SCrou~OP Minas
BUIIB, MONT. January 30. 1951
Corrections In my paper entitled “Purified Woad Fiber. A Study of the Physical and Chemical Properties,” IND.END.CWEM.,23, 131 (1931). the following corrections should be made: The first sentence i t the Method for Determining Copwr Number should read A 3-gram sample of bone-dry shredded nuln is “laced in a 1.5-liter routdlrottomed ffa3k. a wateria&t&’reRux condenser is attached to the flask, 2.50 cc. of iuatw are‘added, and the pulp suspension is quickly brought to the boiling point.” I n the last part of this same method, the liberated iodine is Litrated with 0.20 N sodium thiosulfate. instead of 20 N sodium thiosulfate.
Figure 3
Wc fitvur acetone iwtrad of water for the eiutriatiori of con centrztes, even though the sulljdes may be deadened sufficiently for water elutriation so that there is no danger of inaccuracies from flotation of coarse particles. In addition to tlie fact that elutriation is more rapid in acetone than in water, owing to the Iosv viscosity of acetone, that method gives ckaiier products since it removes effectively any slime coatings from the surface of mincral p;utieles. Since our paper was submitted for publication, another t y w of elutriator (Figure 3) liaz heen put in use for sizing with acetone.
In my paper entitled “Purified Woad Fiber. The PaperMaking Characteristics of Wood Fiber High in Alpha-Cellulose,” IND. ENG. CHEM, 23, 266 (1931), the following comctions should be made: The last Sentence of the synopsis should read: “The presence of suljite wood pulp imparts physical weakness, particularly in
rrspect to tearing resistance and fold endurance.” On page 266, under “Beating in Ball Nlills,” the reference to Figures 1 and 2 should be deleted from the second sentence. On page 267 the caption under Figures 1 and 2 applies only to Figure 1. Figure 2 should be described as “Experimental Paper Machine of the Brown Company.” On page 271, the reference to Figure 8 should be deleted trom the third line above the table in the first column. Figure 4,turn right side to bottom. GBO A. KICETER
