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Old 24th April 2020, 03:13 PM
robinb robinb is offline
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Default 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
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Old 24th April 2020, 04:28 PM
Lostlabours Lostlabours is offline
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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
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Old 24th April 2020, 05:00 PM
robinb robinb is offline
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Thanks Ian

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

best


robin
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Old 25th April 2020, 06:46 AM
Martin Rick Martin Rick is offline
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Quote:
Originally Posted by robinb View Post
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?
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  #5  
Old 25th April 2020, 06:51 AM
robinb robinb is offline
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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 ...
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Old 25th April 2020, 07:26 AM
Lostlabours Lostlabours is offline
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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

Last edited by Lostlabours; 25th April 2020 at 07:52 AM. Reason: add
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