Australia's Science Forum

Our chem students are doing gravimetric analysis and I need to update our vacuum filtration. We have a little pump attached to a tap which works well with individual flasks but is very water wasting.
We have a large vacuum pump used with bell jars and I was wondering if any of you have anything that can attach to this pump and filter a number of flasks.
Lada

Lada,

You cannot use the vacuum pump for this purpose - the vacuum produced by the pump is to high and will suck what you are trying to filter into the flask (and maybe even the paper). Also you have to be very careful not to get water unto the pump.

I know the water pumps are water wasteful but they have about the right ammount of suction. The water tap does not really need to be turned full on, only needs some water flowing through the pump to get enough of a suction.

So, not an ideal answer but I cannot think of any better at the moment.

Cheers
Ross

We use hand operated vacuum pumps (originally bought for E coli determination). They are in the current Science Supply catalogue on page 89. They aren't cheap, but ours have lasted twenty years and are still going strong.

And they're entirely portable!

Thanks, that is exactly what we need.
Karma is coming your way
lada

Hi
I've a teacher who wants to do this and is asking for scintered glass crucibles. Any ideas on what they are and where I'll find them?
Cheers Krysia

They are called Gooch crucibles and you can get them from science supply.
Cat No; 25 85134 and the cost about $40 each. There are cheaper models but I have the schott duran ones and they seem very good. If you have the catalogue see page 22 thet are listed under crucibles.

Sintered glass crucibles are used with filtration flasks to filter very fine particles. The filtration flasks are connected to venturi pumps that use water as the source of suction. I think a lot of us are doing the prac at the moment . ie Sulfate in Fertiliser.
I purchased some sintered glass crucibles in '07 from Science Supply Australia at around $25. Cheapest price, as these things can get quite expensive. You have to buy the Guko rubber gasket as well. These fit into the flask, and then the crucible sits in that.
Lada, I've just run through the prac that was on here somewhere that uses agar as a coagulating agent and it gave good results. I just filtered with filter paper (No 42) and a filter funnel. No need for pumps. (I was a bit concerned as well about the water wasted) I've suggested we try this method next year.