Film and Darkroom User

Film and Darkroom User (http://www.film-and-darkroom-user.org.uk/forum/index.php)
-   Chemical formulae (http://www.film-and-darkroom-user.org.uk/forum/forumdisplay.php?f=41)
-   -   how to convert from pentahydrate to anhydrous (http://www.film-and-darkroom-user.org.uk/forum/showthread.php?t=13158)

robinb 24th April 2020 03:13 PM

how to convert from pentahydrate to anhydrous
 
Hi

I'm trying to make a developer which needs 2g of sodium thiosulphate pentahydrate but I have the anhydrous version

how much anhydrous is equivalent the pentahydrate version ?

thanks

robin

Lostlabours 24th April 2020 04:28 PM

It's 1.274g but you could round that to 1.3g.

It's not one in my conversions spreadsheet so I'll add it, the figure's accurate as it's calculated from the Molecular weights and Kodak had a rule of thumb of 64% for motion picture labs.

I've never seen the anhrous version.

Ian

robinb 24th April 2020 05:00 PM

Thanks Ian

I bought it ages ago from Silverprint when they were in London

best


robin

Martin Rick 25th April 2020 06:46 AM

Quote:

Originally Posted by robinb (Post 132699)
Hi

I'm trying to make a developer which needs 2g of sodium thiosulphate pentahydrate but I have the anhydrous version

how much anhydrous is equivalent the pentahydrate version ?

thanks

robin

Sodium thiosulfate in a developer?

robinb 25th April 2020 06:51 AM

Thats what I thought as well Martin

its a modified version of d72 for colour paper reversal and apparently acts as a restrainer but I'm no chemist
I notice there is a Typo in the amounts
its actually 0.2g per 1000ml

I'm presently struggling to measure so little ...

Lostlabours 25th April 2020 07:26 AM

You don't measure so little you make up a 1% or 10% solution (of the Pentahydrate equivalent).

Are you sure the 0.2g per 1000ml/litre isn't the typo, usually the sodium Thiosulphate is used in the First Developer for reversal at between 4 to 12g per litre. Actually Potassium Thiocyanate is more commonly used.

A 10% solution of Pentahydrate would be 100g in 1 litre, 1% 10g per litre, so with Anhydrous that's 63.7g per litre for 10%, 6.37g/l for 1%.

I'd mix 10%, then i it's 10x in ml the dry weight in gms, so the 0.2g would require 2ml. 10% Thiousulphate solution is always handy for Farmers reducer etc.

Just checked and it is in the region of 0.2-0.3g/l Thioslphate in RA-4 reversal so not a typo.

Ian


All times are GMT. The time now is 08:59 AM.

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.