For hours tonight I have worked out a plan with chemists and research, I will use it tomorrow.
Potassium Chloride (KCI) is available in most countries, it's important to take the food grade powder one, 100% purity.
Then some bicarbonate soda is necessary like Dr Oetker one for baking, now it's important to differentiate because sodium carbonate and sodium bicarbonate are different.
Dissolving the powders in water:
Potassium Chloride KCI solubility in water is 34g/100ml, meaning 1g of KCI must be dissolved in 2.95ml of water or saline solution 0.9 NaCL. It takes 10-20 mins to dissolve without stirring.
Sodium bicarbonate solubility in water is 9.6g per 100ml of water, 1g of it dissolves in 10.41ml of water. It takes 10-15 minutes to dissolve without stirring.
Sodium carbonate (E500) solubility is 35g per 100ml of water so 1g must be dissolved in 2.85ml of water and it takes 20 minutez without stirring.
You can not dissolve those powder products in less water than they need. The concentration will be wrong and it puts you at risk of failure and severe damages.
Steps here according to 22g of KCI which is lethal when injected by intravenous cannula fastly:
1. Mix 22g of KCI (potassium powder) into 65ml of room temperature water and let it rest for 25-30 to fully dissolve without stirring. It must be a liquid with no powder left or visible.
2. Get some PH test paper on Amazon as you will now need to buffer (make less acidic) the potassium solution otheexise it hurts like hell.
Test the solution and use the PH color chart to determine the PH (Google images).
3. If you are using sodium carbonate like the Dr Oetker bicarbonate soda, you need to add very slowly up to 130mg of it into the solution, but do it very slowly and test a lot every time until you reach a Ph between 7 and 7.5 according to color chart.
Between each addition you need to stir a lot to dissolve it fast and may have to wait 5-10 minutes otherwise your PH result will be false.
If you are using sodium bicarbonate (look at the ingredients in the product you have and search it online to make sure), then put a minimum of 5.46mg of it into the solution and wait 10 mins for dissolution, test the Ph and add more very slowly if needed for the same target as above. The max you can add is 10.92mg of it.
4. Your solution is now ready, it should not hurt your veins as you buffered the solution PH, wait further 10 minutes to make sure it's all well dissolved and stir it before putting in a syringe (possible a 70ml syringe, with luer lock).
5. Insert a cannula in the biggest vein you can find in your arm, not your hand, learn vigorusly to do it on YouTube, you can buy them online with a Google search, I advise to take size 18g for fast flow, nothing smaller than 20g, anything below 18g will be very hard to put in a vein. Secure the cannula with strong dressings and flush it with saline solution (you can buy, it's called saline solution pods on Amazon), if it flushes well the cannula is in your vein and you are good to go, if it hurts and swells the cannula is not in a vein so do it again.
6. Shake the solution again in the syringe, lie down, and connect the syringe to the cannula, and you can inject it the faster possible but at a constant rate to ensure you don't break your vein. You heart shall stop within seconds, so it's important to be fast but consistent.
Potassium KCI stops the heart within seconds or minutes, and is only that lethal when injected into a vein, orally it's impossible to drink and requires a huge dose. It can be painful to inject but as it's buffered it's tolerable.
You can buy tourniquets, cannula, dressings, syringes on some websites you can find on Google (Google shopping for example) and saline pods you can find them on Amazon usually for eye irrigation or baby care.
Better make the solution in plastic glasses.
I hope this helps.