TANNING. 145 



Bleaching Paper. — After bleaching the pulp by chloride of 

 lime, small quantities of this salt or chlorine remain in the 

 paper, tending to injure its quality. It is entirely removed 

 by sulphite of soda, which is converted by chlorine and water 

 into muriate and sulphate of soda. Sulphite of lime, or, better 

 still, a stale solution of sulphide of calcium, would probably 

 answer the purpose as well. — J. C. B. 



Water-proof Paper. — J. Bossy prepares such paper by treat- 

 ing half-stuff alternately with soapsuds and a solution of sul- 

 phate of alumina, which results in producing an aluminous 

 soap in the pulp. The sheets, after drying, are sized with glue, 

 rosin-soap, &c. (Rep. Pat. Inv. Aug. 1846.) 



Tracing Paper. — A paper dipped into a thick solution of 

 gum arable and pressed between two dry sheets, renders the 

 three transparent. When dry, it is every way superior for 

 tracing purposes, as it can be written or painted upon. Like 

 the oiled paper, to which it is every way su2:)erior, it impresses 

 the traced lines upon linen or paper. (Chemist, 1850.) 



Tanning. — The ancient process of tanning requiring a long 

 period of time to produce leather, numerous processes have 

 been latterly set forth, and many of them tried on a working 

 scale, for the purpose of shortening this lapse of time. Al- 

 though the end has been attained in a variety of ways, yet 

 the quality of the leather has proved so inferior, that the 

 slower process is still preferred for the finer qualities. The 

 deterioration has been nearly, but not however quite, in direct 

 proportion to the reduction of time in tanning, so that we may 

 hope that methods will be devised for shortening the time 

 without losing in quality. It is true that we are not thoroughly 

 acquainted with the exact nature and progress of the change 

 which a hide undergoes in its transformation, but we believe, 

 on sufficient grounds, that it consists in the simultaneous 

 metamorphosis of the hide into a gelatinous material and its 

 combination with tannin. In some kinds of tanning-, alumina, 

 or an aluminous salt, seems to act the part of tannin. It has 

 been found that an elevated temperature hastens the trans • 

 formation ; that strong liquors, or the injection of liquors by 

 N 10 



