It was the third day of Butter Week when Vera Valentinova collapsed as she entered their room, dropped her heavy wicker basket and remained where she fell, her shoulders shaking, her red hands pressed to her narrow face. Kneeling on his mattress, Konstantin watched as the old soldier, Viktor, lifted her carefully and sat her on the stool beside the stove. He glanced down to see his mixture of copper oxide and sulphuric acid resolve itself into a deep blue copper sulphate solution - as The Principles of Chemistry had predicted. With a breath, he extinguished the kerosene burner and hurried into the room.